Mine is the same. Every device in my home updated to 16.4. Upgraded to new HomeKit architecture last night and now all I get when I try to airplay to any of my four HomePods is "AirPlay Unable to connect to..."
I have rebooted everything. Everything is on the latest firmware (required in order to update to the new HomeKit architecture)
Would love if someone has a fix because this is all broken.
Also Airplay to my TV and Sonos doesn't work and they are also on the latest firmware.