I have a Pixel 4a 5G, which still works great but it's nearing the end of security updates. I see a lot of options on listicle articles, but I'm curious to hear from some real people
GrapheneOS flashes fine on the 4a 5G, just did one for my wife last week. Can't say I'm happy with the theme they use, but that's a minor quibble. Keep in mind, there is no google play store on it. It's degoogled. You can set up Fdroid and then use that to install Aurora Store that will give you a bunch of the Play apps. But things that rely on Google Play Services might not work.
Very easy to convert back to factory image, there's a link in the install procedure to jump back to stock (which is all done via a Chromium based browser's USB port access).
Doesn't hurt to stick with PixelExperience, put it on an old 2XL and gave it to my sister and she uses it as her main device. Basically stock pixel (hence the name) but community updated with security patches & new releases
if the graphene leadership is a worry then calyx os and if you hate the graphene leadership so much that you want to have a source available os then copperhead os
I have Calyxos on my 4a5g. They intend to support it until January 2025. Earlier I had Lineageos installed and was very happy with that, too, but the updates were a bit slow.