I recently bought a second hand Pixel 6 and installed GrapheneOS on it.
Couldn't be happier. Surprisingly it's one of the most straightforward ROMs I've used, and I've used many over the years.
> ... most straightforward ROMs I've used ...
ahem I believe GrapheneOS is an OS, and not a ROM... The project founder really wants you to use the "right" terminology: https://news.ycombinator.com/item?id=33567842 ;)