Needed to implement Open Recent on Mac Catalyst. See https://speakerdeck.com/steipete/shipping-a-mac-catalyst-app-the-good-the-bad-and-the-ugly

AppKitHelper.m

@implementation UIImage (ResourceProxyHack)

+ (UIImage *)_iconForResourceProxy:(id)proxy format:(int)format {
    // HACK: proxy seems garbage so we always show PDF for now.
    let cgImage = [_bridge imageForFileType:@"pdf"];
    // HACK: We use mainScreen here but could have multiple screens.
    let image = [UIImage imageWithCGImage:cgImage scale:UIScreen.mainScreen.scale orientation:UIImageOrientationUp];
    return image;
}

@end

// In the AppKit bridge:
- (CGImageRef)imageForFileType:(NSString *)fileType {
  NSImage *image = [NSWorkspace.sharedWorkspace iconForFileType:fileType];
  image.size = NSMakeSize(16, 16);
  CGImageRef cgRef = [image CGImageForProposedRect:NULL context:nil hints:nil];
  return cgRef;
}