I like what GrapheneOS is doing, but it's focused on having the absolute best security rather than supporting a lot of phones. If you aren't wanted by three letter agencies then LineageOS is good enough
Keep in mind, you don't have to be an activist or journalist to get targeted with sophisticated spyware. This very recent Lemmy post is a great example: https://slrpnk.net/post/15858999
It seems to apply to all third party operating systems. I pretty much have to use stock or I can't use my bank apps, can't use my phone to prove I'm me when remote logging in to work
I used to use cyanogen then lineage until security stuff made the phone too useless.
I bought my current phone specifically because it was supported by LineageOS. Before that I used an unsupported Samsung phone, which was such a shitty experience that I made a promise to myself that my next phone has to have custom ROMs available