LineageOS supports the Google Pixel 3 with LineageOS 18.1 (aka Android 11). It's definitely worth giving this a shot and you can revert to the standard Google release if you'd like. Word of warning on Verizon devices, though. If you bought from Verizon, they generally place an OEM lock on it. So, the device is "unlocked" in terms of carrier, but locked in terms of OS. Don't buy Pixels from Verizon.
I did this on my Pixel 2, but unless I’m mistaken you have to unlock the boot loader to do it, leaving your device completely unsecured if someone has physical access to it.
I gave up and got a phone from a manufacturer who provides true 6+ year security support. I was surprised to find that iPhone was essentially the only option.
In what sense is it completely unsecured? As far as I can tell the data partition at least is protected and installing another OS should require wiping this partition.
I mean given unfettered physical access someone could conceivably install malicious hard/software in it which might spy on you in other ways, but it takes some very strict security requirements for that to be an issue.
LineageOS is cool and can prolong the device usability but some apps may not work (Google Pay, banking apps) if they detect an unofficial system (via SafetyNet). And you likely won't get future vendor blob upgrades (from Qualcomm), not improving the security risk problem.
Hm.. i wonder if i can roll back to before Google completely changed all the UI a few months ago. That alone almost made me throw it out and buy an iPhone
How To: https://wiki.lineageos.org/devices/blueline/install
Download: https://download.lineageos.org/blueline