HMMM? This is interesting and perhaps an indication of the parallel code development between iOS/iPadOS/MacOS and Apple's code once, run everywhere development platform.
My Apple ID Password so far has worked everywhere I have tried it (including Music, iCloud, and Mail) in all three OS variants except in App Store on any of my beta running devices. As a reality check it still works in App Store if I reboot my MBP into Mojave. This is why early beta testing is not for everyone. 😜
