Mp3Tag can see flac tags, including key. I assume Metadata++ can see it, cause it can see everything. My DAW FL Studio can’t see anything cause it rides the special bus. Resonic Pro can see them. Dark Audacity can see it. I don’t see much fields in Music Bee; just some basic ones, that it can see. Probably because it’s only for music consumption. Probably the same with MusicBrianz services and JaiKoz etc.