Hi OP, I am in a similar situation as you were so I wonder which solution you chose at the end and if you are happy with it?

CalyxOS still provides extended support for Pixel 4a until August 2024.

You could try to change the sleep state from s2idle to deep. Not sure how to do this on Kubuntu though.

I second using a preconfig for Hyprland if you want to have something fancy and usable out of the box. You can build on top of that.

Fairphone

That’s already possible either by using a custom ROM or by connecting to a PC and using adb.