Ok I think I have a solution for you people - at least these steps seem to work for me:
Setup - two Homepods and one Apple TV connected to LGTV with optical connection to two KRK monitors. All in different rooms (configured with Home app on iPhone iOS14.5)
After upgrading all devices to 14.5 - Homepods were out of sync with ATV/KRK - I hav previously factory reset all devices and couldn't get SYNC working as it was before 14.5 upgrade!!!!!
So, this is my recollection of the steps to getSYNC working - good luck, I hope this works for you
I moved the Homepods next to the ATV, and used Home app to configure Homepods into the same room (living room) and also configured as "paired".
Then I set the ATV to use the Homepods as audio out (ATV Settings - Video & Audio - Default Audio Output - Select - Homepods
Played some ATV through them and while a show was playing, next step,
From iPhone I played music and directed the music to the Airplay - in my case the "Living Room" (which was Homepods-Pair) and then added the ATV speakers to the airplay list and F-me it played in sync.
Then I un-paired the Homepods - still all in sync
Then moved the Homepods back to different rooms and I can airplay to all three devices IN SYNC - F-yeh
It sounds awesome again with ODESZA filling the place with music IN SYNC