Custom ringtones - iOS 15 and macOS 12 - how to get a song or ringtone onto iPhone

Have searched all over, and can't figure it out. Not using 3rd party apps, just the Apple included apps. I have recorded some stuff from movies with Voice Memos app on iPhone. I take these clips and email to myself, then open on Mac and then convert file from m4a to m4r so they are in the ringtone format. Can't figure out how then to get them into the ringtone list in the iPhone Sound settings. The Voice Memos app lets me edit recordings (both Mac and iPhone), and I seem to recall years ago you could just add these to iTunes and sync them over USB to your iPhone, then select them, or select a song form iTunes and make a clip and use that as a ringtone. Now with Music replacing iTunes I have no clue. Tried manually managing music instead of automatically syncing the Music library, thought I could drag and drop the file onto the iPhone in the Finder, that didn't work either.

The GarageBand method I just can't follow either.

Any help much appreciated. Cheers!