diff --git a/engine/src/flutter/fml/BUILD.gn b/engine/src/flutter/fml/BUILD.gn
index 0b1ff30be08..fb66f7ffafc 100644
--- a/engine/src/flutter/fml/BUILD.gn
+++ b/engine/src/flutter/fml/BUILD.gn
@@ -135,18 +135,13 @@ source_set("fml") {
   libs = []
 
   if (is_ios || is_mac) {
-    sources += [ "platform/darwin/concurrent_message_loop_factory.mm" ]
-  } else {
-    sources += [ "concurrent_message_loop_factory.cc" ]
-  }
-
-  if (is_ios || is_mac) {
-    cflags_objc = flutter_cflags_objc
-    cflags_objcc = flutter_cflags_objcc
+    cflags_objc = flutter_cflags_objc_arc
+    cflags_objcc = flutter_cflags_objcc_arc
 
     sources += [
       "platform/darwin/cf_utils.cc",
       "platform/darwin/cf_utils.h",
+      "platform/darwin/concurrent_message_loop_factory.mm",
       "platform/darwin/message_loop_darwin.h",
       "platform/darwin/message_loop_darwin.mm",
       "platform/darwin/paths_darwin.mm",
@@ -163,6 +158,8 @@ source_set("fml") {
     ]
 
     frameworks = [ "Foundation.framework" ]
+  } else {
+    sources += [ "concurrent_message_loop_factory.cc" ]
   }
 
   if (is_android) {
@@ -365,7 +362,10 @@ if (enable_unittests) {
       "time/time_unittest.cc",
     ]
 
-    if (is_mac) {
+    if (is_mac || is_ios) {
+      cflags_objc = flutter_cflags_objc_arc
+      cflags_objcc = flutter_cflags_objcc_arc
+
       sources += [
         "platform/darwin/cf_utils_unittests.mm",
         "platform/darwin/string_range_sanitization_unittests.mm",
diff --git a/engine/src/flutter/impeller/BUILD.gn b/engine/src/flutter/impeller/BUILD.gn
index 3bd0a09c828..0f8b679abea 100644
--- a/engine/src/flutter/impeller/BUILD.gn
+++ b/engine/src/flutter/impeller/BUILD.gn
@@ -60,7 +60,6 @@ impeller_component("impeller_unittests") {
     "core:allocator_unittests",
     "display_list:skia_conversions_unittests",
     "geometry:geometry_unittests",
-    "renderer/backend/metal:metal_unittests",
     "runtime_stage:runtime_stage_unittests",
     "shader_archive:shader_archive_unittests",
     "tessellator:tessellator_unittests",
@@ -80,6 +79,10 @@ impeller_component("impeller_unittests") {
     ]
   }
 
+  if (impeller_enable_metal) {
+    deps += [ "//flutter/impeller/renderer/backend/metal:metal_unittests" ]
+  }
+
   if (impeller_enable_vulkan) {
     deps += [ "//flutter/impeller/renderer/backend/vulkan:vulkan_unittests" ]
   }
diff --git a/engine/src/flutter/shell/common/BUILD.gn b/engine/src/flutter/shell/common/BUILD.gn
index a2cd2be4834..96133165d20 100644
--- a/engine/src/flutter/shell/common/BUILD.gn
+++ b/engine/src/flutter/shell/common/BUILD.gn
@@ -296,14 +296,14 @@ if (enable_unittests) {
     }
 
     if (test_enable_metal) {
+      cflags_objc = flutter_cflags_objc_arc
+      cflags_objcc = flutter_cflags_objcc_arc
+
       sources += [
         "shell_test_platform_view_metal.h",
         "shell_test_platform_view_metal.mm",
       ]
 
-      cflags_objc = flutter_cflags_objc_arc
-      cflags_objcc = flutter_cflags_objcc_arc
-
       public_deps += [ "//flutter/shell/platform/darwin/graphics" ]
     }
   }
diff --git a/engine/src/flutter/shell/gpu/BUILD.gn b/engine/src/flutter/shell/gpu/BUILD.gn
index ed3dbfbf5b9..8d216d16c79 100644
--- a/engine/src/flutter/shell/gpu/BUILD.gn
+++ b/engine/src/flutter/shell/gpu/BUILD.gn
@@ -71,6 +71,9 @@ source_set("gpu_surface_vulkan") {
 
 if (shell_enable_metal) {
   source_set("gpu_surface_metal") {
+    cflags_objc = flutter_cflags_objc_arc
+    cflags_objcc = flutter_cflags_objcc_arc
+
     sources = [
       "gpu_surface_metal_delegate.cc",
       "gpu_surface_metal_delegate.h",
@@ -80,9 +83,6 @@ if (shell_enable_metal) {
       "gpu_surface_noop.mm",
     ]
 
-    cflags_objc = flutter_cflags_objc_arc
-    cflags_objcc = flutter_cflags_objcc_arc
-
     public_deps = gpu_common_deps
 
     if (impeller_enable_metal) {
@@ -99,6 +99,9 @@ if (shell_enable_metal) {
 if (is_mac) {
   impeller_component("gpu_surface_metal_unittests") {
     testonly = true
+    cflags_objc = flutter_cflags_objc_arc
+    cflags_objcc = flutter_cflags_objcc_arc
+
     target_type = "executable"
     sources = [
       "gpu_surface_metal_impeller_unittests.mm",
diff --git a/engine/src/flutter/shell/platform/darwin/common/BUILD.gn b/engine/src/flutter/shell/platform/darwin/common/BUILD.gn
index 58638a5bc09..459f473909d 100644
--- a/engine/src/flutter/shell/platform/darwin/common/BUILD.gn
+++ b/engine/src/flutter/shell/platform/darwin/common/BUILD.gn
@@ -111,6 +111,9 @@ test_fixtures("framework_common_fixtures") {
 # Unit tests for channels.
 executable("framework_common_unittests") {
   testonly = true
+  cflags_objc = flutter_cflags_objc_arc
+  cflags_objcc = flutter_cflags_objcc_arc
+  ldflags = [ "-ObjC" ]
 
   sources = [
     "framework/Source/FlutterBinaryMessengerRelayTest.mm",
@@ -119,10 +122,6 @@ executable("framework_common_unittests") {
     "framework/Source/flutter_standard_codec_unittest.mm",
   ]
 
-  cflags_objcc = flutter_cflags_objcc_arc
-
-  ldflags = [ "-ObjC" ]
-
   deps = [
     ":framework_common",
     ":framework_common_fixtures",
diff --git a/engine/src/flutter/shell/platform/darwin/macos/BUILD.gn b/engine/src/flutter/shell/platform/darwin/macos/BUILD.gn
index 3ce4bfc1f0a..1274f1c4d87 100644
--- a/engine/src/flutter/shell/platform/darwin/macos/BUILD.gn
+++ b/engine/src/flutter/shell/platform/darwin/macos/BUILD.gn
@@ -52,6 +52,8 @@ _flutter_framework_headers_copy_dir =
 
 source_set("flutter_framework_source") {
   visibility = [ ":*" ]
+  cflags_objc = flutter_cflags_objc_arc
+  cflags_objcc = flutter_cflags_objcc_arc
 
   sources = [
     "framework/Source/AccessibilityBridgeMac.h",
@@ -141,8 +143,6 @@ source_set("flutter_framework_source") {
     "FLUTTER_ENGINE_NO_PROTOTYPES",
   ]
 
-  cflags_objcc = flutter_cflags_objcc_arc
-
   frameworks = [
     "Carbon.framework",
     "Cocoa.framework",
@@ -173,6 +173,9 @@ test_fixtures("flutter_desktop_darwin_fixtures") {
 
 executable("flutter_desktop_darwin_unittests") {
   testonly = true
+  cflags_objc = flutter_cflags_objc_arc
+  cflags_objcc = flutter_cflags_objcc_arc
+  ldflags = [ "-ObjC" ]
 
   sources = [
     "framework/Source/AccessibilityBridgeMacTest.mm",
@@ -205,10 +208,6 @@ executable("flutter_desktop_darwin_unittests") {
     "framework/Source/TestFlutterPlatformView.mm",
   ]
 
-  cflags_objcc = flutter_cflags_objcc_arc
-
-  ldflags = [ "-ObjC" ]
-
   deps = [
     ":flutter_desktop_darwin_fixtures",
     ":flutter_framework_source",
diff --git a/engine/src/flutter/shell/platform/embedder/BUILD.gn b/engine/src/flutter/shell/platform/embedder/BUILD.gn
index de450dc5ed4..a0c1b25899b 100644
--- a/engine/src/flutter/shell/platform/embedder/BUILD.gn
+++ b/engine/src/flutter/shell/platform/embedder/BUILD.gn
@@ -144,6 +144,9 @@ template("embedder_source_set") {
     }
 
     if (embedder_enable_metal) {
+      cflags_objc = flutter_cflags_objc_arc
+      cflags_objcc = flutter_cflags_objcc_arc
+
       sources += [
         "embedder_external_texture_metal.h",
         "embedder_external_texture_metal.mm",
@@ -159,9 +162,6 @@ template("embedder_source_set") {
         deps += [ "//flutter/impeller/renderer/backend/metal" ]
       }
 
-      cflags_objc = flutter_cflags_objc_arc
-      cflags_objcc = flutter_cflags_objcc_arc
-
       deps += [ "//flutter/shell/platform/darwin/graphics" ]
     }
 
@@ -375,6 +375,9 @@ if (enable_unittests) {
     }
 
     if (test_enable_metal) {
+      cflags_objc = flutter_cflags_objc_arc
+      cflags_objcc = flutter_cflags_objcc_arc
+
       sources += [ "tests/embedder_metal_unittests.mm" ]
     }
 
diff --git a/engine/src/flutter/shell/platform/embedder/tests/embedder_metal_unittests.mm b/engine/src/flutter/shell/platform/embedder/tests/embedder_metal_unittests.mm
index 3f5ec9e549d..d59c92bf62c 100644
--- a/engine/src/flutter/shell/platform/embedder/tests/embedder_metal_unittests.mm
+++ b/engine/src/flutter/shell/platform/embedder/tests/embedder_metal_unittests.mm
@@ -65,7 +65,7 @@ static sk_sp<SkSurface> GetSurfaceFromTexture(const sk_sp<GrDirectContext>& skia
                                               SkISize texture_size,
                                               void* texture) {
   GrMtlTextureInfo info;
-  info.fTexture.reset([(id<MTLTexture>)texture retain]);
+  info.fTexture.retain(texture);
   GrBackendTexture backend_texture = GrBackendTextures::MakeMtl(
       texture_size.width(), texture_size.height(), skgpu::Mipmapped::kNo, info);
 
diff --git a/engine/src/flutter/testing/BUILD.gn b/engine/src/flutter/testing/BUILD.gn
index 54bdcf40009..2da76f07d75 100644
--- a/engine/src/flutter/testing/BUILD.gn
+++ b/engine/src/flutter/testing/BUILD.gn
@@ -190,7 +190,12 @@ if (enable_unittests) {
 # On iOS, this is enabled to allow for Metal tests to run within a test app
 if (is_mac || is_ios) {
   source_set("metal") {
+    testonly = true
+
     if (shell_enable_metal) {
+      cflags_objc = flutter_cflags_objc_arc
+      cflags_objcc = flutter_cflags_objcc_arc
+
       sources = [
         "test_metal_context.h",
         "test_metal_context.mm",
@@ -210,11 +215,6 @@ if (is_mac || is_ios) {
         deps += [ "//flutter/vulkan" ]
       }
     }
-
-    cflags_objc = flutter_cflags_objc_arc
-    cflags_objcc = flutter_cflags_objcc_arc
-
-    testonly = true
   }
 }
 
diff --git a/engine/src/flutter/third_party/accessibility/BUILD.gn b/engine/src/flutter/third_party/accessibility/BUILD.gn
index b5eb256f4dd..9cdc8e827c1 100644
--- a/engine/src/flutter/third_party/accessibility/BUILD.gn
+++ b/engine/src/flutter/third_party/accessibility/BUILD.gn
@@ -76,6 +76,10 @@ if (enable_unittests) {
       ]
 
       if (is_mac) {
+        cflags_objc = flutter_cflags_objc_arc
+        cflags_objcc = flutter_cflags_objcc_arc
+        ldflags = [ "-ObjC" ]
+
         sources += [ "ax/platform/ax_platform_node_mac_unittest.mm" ]
         frameworks = [
           "AppKit.framework",
@@ -84,10 +88,6 @@ if (enable_unittests) {
           "CoreText.framework",
           "IOSurface.framework",
         ]
-
-        cflags_objc = flutter_cflags_objc_arc
-        cflags_objcc = flutter_cflags_objcc_arc
-        ldflags = [ "-ObjC" ]
       }
       if (is_win) {
         sources += [
diff --git a/engine/src/flutter/third_party/accessibility/ax/BUILD.gn b/engine/src/flutter/third_party/accessibility/ax/BUILD.gn
index a4e366615ff..eb1a950e8e9 100644
--- a/engine/src/flutter/third_party/accessibility/ax/BUILD.gn
+++ b/engine/src/flutter/third_party/accessibility/ax/BUILD.gn
@@ -82,12 +82,13 @@ source_set("ax") {
   ]
 
   if (is_mac) {
+    cflags_objc = flutter_cflags_objc_arc
+    cflags_objcc = flutter_cflags_objcc_arc
+
     sources += [
       "platform/ax_platform_node_mac.h",
       "platform/ax_platform_node_mac.mm",
     ]
-    cflags_objc = flutter_cflags_objc_arc
-    cflags_objcc = flutter_cflags_objcc_arc
   } else if (is_win) {
     sources += [
       "platform/ax_fragment_root_delegate_win.h",