Trouble using HomePod as audio output w/ new appletv update

My appletv updated itself, and I can no longer find an option to link it to my HomePod (as a stereo). I made sure to group both accessories in the same “home” room, but the promised “use HomePod as stereo” window has not popped up (after multiple restarts). The manual “choose audio output” option seems to have vanished from the audio settings, too. Any help would be appreciated.