diff --git a/packages/react-native/React/Base/RCTUtils.h b/packages/react-native/React/Base/RCTUtils.h
index a26b1a7a5fc6..b06b279593fe 100644
--- a/packages/react-native/React/Base/RCTUtils.h
+++ b/packages/react-native/React/Base/RCTUtils.h
@@ -141,6 +141,10 @@ RCT_EXTERN NSURL *RCTDataURL(NSString *mimeType, NSData *data);
 // Gzip functionality - compression level in range 0 - 1 (-1 for default)
 RCT_EXTERN NSData *__nullable RCTGzipData(NSData *__nullable data, float level);
 
+// Determines whether data is already gzipped. Declared here (rather than only in
+// RCTUtils.mm) so it keeps C linkage and can be called from .m unit tests.
+RCT_EXTERN BOOL RCTIsGzippedData(NSData *__nullable data);
+
 // Returns the relative path within the main bundle for an absolute URL
 // (or nil, if the URL does not specify a path within the main bundle)
 RCT_EXTERN NSString *__nullable RCTBundlePathForURL(NSURL *__nullable URL);
diff --git a/packages/react-native/React/Base/RCTUtils.mm b/packages/react-native/React/Base/RCTUtils.mm
index a378d0001e7a..7ea31c9702e2 100644
--- a/packages/react-native/React/Base/RCTUtils.mm
+++ b/packages/react-native/React/Base/RCTUtils.mm
@@ -761,7 +761,6 @@ BOOL RCTForceTouchAvailable(void)
                                                [data base64EncodedStringWithOptions:(NSDataBase64EncodingOptions)0]]];
 }
 
-BOOL RCTIsGzippedData(NSData *__nullable /*data*/); // exposed for unit testing purposes
 BOOL RCTIsGzippedData(NSData *__nullable data)
 {
   UInt8 *bytes = (UInt8 *)data.bytes;
diff --git a/packages/rn-tester/RNTester-macOS/RNTester-macOS.xctestplan b/packages/rn-tester/RNTester-macOS/RNTester-macOS.xctestplan
index b4aa08079c2e..91420d67276a 100644
--- a/packages/rn-tester/RNTester-macOS/RNTester-macOS.xctestplan
+++ b/packages/rn-tester/RNTester-macOS/RNTester-macOS.xctestplan
@@ -2,12 +2,9 @@
   "configurations" : [
     {
       "id" : "59C4DFC4-597F-41C6-99FD-32D94C5488D4",
-      "name" : "Address Sanitizer",
+      "name" : "Default",
       "options" : {
-        "addressSanitizer" : {
-          "detectStackUseAfterReturn" : true,
-          "enabled" : true
-        }
+
       }
     }
   ],
@@ -24,8 +21,7 @@
       "identifier" : "ACC52F3D299ECB7A002A2B0B",
       "name" : "RNTester-macOS"
     },
-    "testRepetitionMode" : "retryOnFailure",
-    "undefinedBehaviorSanitizerEnabled" : true
+    "testRepetitionMode" : "retryOnFailure"
   },
   "testTargets" : [
     {
diff --git a/packages/rn-tester/RNTesterUnitTests/RCTGzipTests.m b/packages/rn-tester/RNTesterUnitTests/RCTGzipTests.m
index a24d9972be77..de848ba8be3a 100644
--- a/packages/rn-tester/RNTesterUnitTests/RCTGzipTests.m
+++ b/packages/rn-tester/RNTesterUnitTests/RCTGzipTests.m
@@ -11,8 +11,6 @@
 #import <React/RCTNetworking.h>
 #import <React/RCTUtils.h>
 
-extern BOOL RCTIsGzippedData(NSData *data);
-
 @interface RCTNetworking (Private)
 
 - (void)buildRequest:(NSDictionary<NSString *, id> *)query completionBlock:(void (^)(NSURLRequest *request))block;
diff --git a/packages/rn-tester/RNTesterUnitTests/RCTImageLoaderTests.m b/packages/rn-tester/RNTesterUnitTests/RCTImageLoaderTests.m
index 6c58e9cb26d0..baedbf966369 100644
--- a/packages/rn-tester/RNTesterUnitTests/RCTImageLoaderTests.m
+++ b/packages/rn-tester/RNTesterUnitTests/RCTImageLoaderTests.m
@@ -7,6 +7,8 @@
 
 #import <XCTest/XCTest.h>
 
+#import <React/RCTUIKit.h> // [macOS]
+
 #import <React/RCTBridge.h>
 #import <React/RCTImageLoader.h>
 
@@ -35,7 +37,7 @@ - (void)setUp
 
 - (void)testImageLoading
 {
-  UIImage *image = [UIImage new];
+  RCTPlatformImage *image = [RCTPlatformImage new]; // [macOS]
 
   id<RCTImageURLLoader> loader = [[RCTImageLoaderTestsURLLoader1 alloc] initWithPriority:1.0
       canLoadImageURLHandler:^BOOL(__unused NSURL *requestURL) {
@@ -70,7 +72,7 @@ - (void)testImageLoading
         XCTAssertEqual(progress, 1);
         XCTAssertEqual(total, 1);
       }
-      partialLoadBlock:^(UIImage *loadedImage) {
+      partialLoadBlock:^(RCTPlatformImage *loadedImage) { // [macOS]
       }
       completionBlock:^(NSError *loadError, id loadedImage) {
         XCTAssertEqualObjects(loadedImage, image);
@@ -80,7 +82,7 @@ - (void)testImageLoading
 
 - (void)testImageLoaderUsesImageURLLoaderWithHighestPriority
 {
-  UIImage *image = [UIImage new];
+  RCTPlatformImage *image = [RCTPlatformImage new]; // [macOS]
 
   id<RCTImageURLLoader> loader1 = [[RCTImageLoaderTestsURLLoader1 alloc] initWithPriority:1.0
       canLoadImageURLHandler:^BOOL(__unused NSURL *requestURL) {
@@ -130,7 +132,7 @@ - (void)testImageLoaderUsesImageURLLoaderWithHighestPriority
         XCTAssertEqual(progress, 1);
         XCTAssertEqual(total, 1);
       }
-      partialLoadBlock:^(UIImage *loadedImage) {
+      partialLoadBlock:^(RCTPlatformImage *loadedImage) { // [macOS]
       }
       completionBlock:^(NSError *loadError, id loadedImage) {
         XCTAssertEqualObjects(loadedImage, image);
@@ -141,7 +143,7 @@ - (void)testImageLoaderUsesImageURLLoaderWithHighestPriority
 - (void)testImageDecoding
 {
   NSData *data = [NSData dataWithBytesNoCopy:blackGIF length:sizeof(blackGIF) freeWhenDone:NO];
-  UIImage *image = [[UIImage alloc] initWithData:data];
+  RCTPlatformImage *image = [[RCTPlatformImage alloc] initWithData:data]; // [macOS]
 
   id<RCTImageDataDecoder> decoder = [[RCTImageLoaderTestsDecoder1 alloc] initWithPriority:1.0
       canDecodeImageDataHandler:^BOOL(__unused NSData *imageData) {
@@ -180,7 +182,7 @@ - (void)testImageDecoding
 - (void)testImageLoaderUsesImageDecoderWithHighestPriority
 {
   NSData *data = [NSData dataWithBytesNoCopy:blackGIF length:sizeof(blackGIF) freeWhenDone:NO];
-  UIImage *image = [[UIImage alloc] initWithData:data];
+  RCTPlatformImage *image = [[RCTPlatformImage alloc] initWithData:data]; // [macOS]
 
   id<RCTImageDataDecoder> decoder1 = [[RCTImageLoaderTestsDecoder1 alloc] initWithPriority:1.0
       canDecodeImageDataHandler:^BOOL(__unused NSData *imageData) {