I use Homeasststant companion APP . After upgrade to 2025030800 I cant open the voice assistant via pressing Home Button on my Pixel 7a. In GOS 2025030300 it worked. I checked this in a different Pixel8 device that is not yet upgraded. Shutdown and repower did not change this issue.

Any idea how to reactivate "Voice-Assist by pressing Home- Button" ?

is it possible the permissions were revoked? Try setting the assistant to 'nothing' in settings, then set HomeAssistant as the assistant again.