Demonstrates a bug in Big Sur (b6) with APFS volumes having non-ASCII names. To reproduce, rename any APFS volume so that it contains an "ü" in it.

main.m

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
	NSArray<NSURL*> *vols = [NSFileManager.defaultManager mountedVolumeURLsIncludingResourceValuesForKeys:nil options:0];
	for (NSURL *url1 in vols) {
		NSURL *url2 = [NSURL fileURLWithPath:url1.path];
		if (! [url1 isEqual:url2]) {
			NSLog(@"url mismatch: %@ - %@", url1, url2);
			if (! [url1.path isEqualToString:url2.path]) {
				NSLog(@"path mismatch: %@ - %@", url1.path, url2.path);
			}
			NSLog(@"url1's VolID: %@", [url1 resourceValuesForKeys:@[NSURLVolumeIdentifierKey] error:nil][NSURLVolumeIdentifierKey]);
			NSLog(@"url2's VolID: %@", [url2 resourceValuesForKeys:@[NSURLVolumeIdentifierKey] error:nil][NSURLVolumeIdentifierKey]);
		}
	}
	return 0;
}

It's curious that while both the NSURLs and their paths do not test as equal, their Volume IDs are equal!

So, obviously, [NSURL isEqual] does not use the NSURLVolumeIdentifierKey for its test. It probably uses the URL's path.

Reported to Apple as FB8695377