When I still had kitties (and a house), I bought a litter box with a lid. I then fashioned a vent hose with a 120mm 12V PCM fan running at low RPM. The hose went through the ceiling in a closet and exhausted out an attic vent. Zero cat box smell and no noise. While my exact implementation isn’t available to everyone (like in apartments), the basics can be adapted to almost any situation.

If the hardware is still great, how about installing LineageOS? Here’s the direct link to LineageOS for the Pixel 4a: https://wiki.lineageos.org/devices/sunfish/. I’ve been using LineageOS on all the old devices which are supported, mostly OnePlus and Nexus devices. Lightweight, and does everything I need.