The only FP4 custom ROM I know of, that has a pre-rooted version is LeOS (forum topic).
But that wasn’t an option for me.
I have experiences with Magisk on a FPOS and a CalyxOS phone and both devices have been running without issues for a year basically (Calyx has only been out for 8 months).
The only thing to look out for are OTA updates, but those are like a minute of additional work, not a problem really 