I have used CyanogenMod, and later LineageOS, for quite some time and was pretty pleased with it. The problem is it seems to be past its prime. It dropped support for mainstream phones more and more and is currenly limited to either very old handsets or rather exotic manufacturers. The most recent Samsung S series they support is from 2014, almost six years ago. CM and LOS were also popular on the Nexus 4 and 5, thes…
I think that's just because stock ROMS have become good enough that we don't need custom ROMS; except for purposes like de-Googling your phone or removing stuff installed by your OEM.
From a security perspective, custom roms are still worth it.