@haui Nice!
You're likely aware but just in case: gnome-calls with SIP should work see https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5505 and the MR linked there.
You could do home assistant lights with #phosh's launcher-box plugin as band aid (e.g. add launchers and use the or progress bar/counter API to indicate on/off)
(a real plugin for homeassistant would be nice though).