i've tested this GSI over camellian:
aosp a12 v400c gsi : system-squeak-arm64-ab-gapps.img.xz have the brightness slider bug, if i power off the mobile cant power on with button, say error mobile not certified for use google services.
lineage 19 a12 gsi : lineage-19.0-20211106-UNOFFICIAL-treble_arm64_bvS.img.xz cant have gapps (can try it after you root and install magisk), have the brightness slider bug, if I power off the mobile cant power on with button.
pixelexperience a12 v400c gsi : PixelExperience_arm64-ab-12.0-20211121-UNOFFICIAL.img.xz
have the brightness slider bug, if i power off the mobile cant power on with button.
SO ALL GSI I HAVE TESTED (A11 in the past OR A12) HAVE THE SAME BUGS, I THINK ARE A BAD MOBILE NOT GSI PROBLEM.
How to fix brightness slider:
Go to phh treble settings,misc settings enable "use alternative brightness scale", "use linear screen brightness slider" and "allow setting brightness to the lowest possible",reboot the device
How to fix bluetooth audio:
Go to phh treble settings,misc settings, "Force enable a2dp off-load" and "Bluetooth workarounds" select mediatek option and reboot the device