If anyone on 14.4 needs to get their battery replaced - good news, the diagnostics they run in the Apple Store run just fine on 14.4 b1. (I got my battery in my iPhone X replaced on Dec 22). (so, at least the diags run properly on the X)
So, yes, they didn't want to do it as I'm running beta code *eye roll*, but I insisted and we went ahead (given how long the wait is to get into one of these stores right now due to Covid, I sure as wasn't going home to downgrade to 14.3 and then come back in the New Year).
Did the iCloud backup while waiting in line outside, connected to the store's wifi. 
So, yes, they didn't want to do it as I'm running beta code *eye roll*, but I insisted and we went ahead (given how long the wait is to get into one of these stores right now due to Covid, I sure as wasn't going home to downgrade to 14.3 and then come back in the New Year).