Installed the Android 12 update as well.
But noticed a weird problem. With Google Clock alarm and timer, the screen won't activate when the alarm goes off. You can only hear the sound. Only when you manually activate the screen (by double tapping or pressing power button) you can see the alarm screen and the buttons (slider). I don't have Do Not Disturb etc. activated.
With Samsung Clock there is no problem. Alarm works normally and activates the screen and sound.
Could you test Google Clock alarm/timer with your phone? Can you verify the possible bug?
I have the same problem since the android 12 update. The timer doesn't go off and goes into minus time and doesn't bleep until you unlock the phone. Please fix it