Yes, I know about GrapheneOS and their loyalty to Google. So you still have to pay Google for the device and then you can install GrapheneOS on it.

I also used CyanogenMod (and the others, AOKP and Paranoid Android and many of their derivatives) back in the day. Tickled fucking pink to see that Paranoid Android still exists. That fork was fun.

I also used a phone where everyone wanted a certain custom ROM for that phone, so bad, that they got together the money and actually bought this guy the phone. He said "suckers," flipped it on Ebay, and that was that. I don't recall if he ever promised to build for us if someone bought him the phone or that was just hopium. I also did not donate to the endeavour. So a phone has to be actively supported by developers, or a developer, and as they themselves get newer phones, they tend to drop older ones. So you're not getting new versions of Android, new features, or even security fixes. Needless to say, I don't trust custom firmware.