Custom ROMs were always a pretty niche thing, and they’ve become much less worth it since:

Stock Android doesn’t suck as much as it used to

Banking Apps aren’t guaranteed to work

VoLTE doesn’t work (this might depend on phone model)

Most manufacturers now offer software support for a reasonable length of time

So unless there’s an old feature you want to keep (LG Quad DAC diehards represent), or you’re super privacy-conscious, most people aren’t going to bother.

or going to a protest

I’d suggest you may be better off not bringing your phone at all, in this case.