Usually you can have 3 kind of rom for an android device:
Default from manufactuerer: usually locked down, shitty default apps and preinstalled crapware, updates stop soon. Usually stable.
Cooked/unofficial rom from xda or telegram: some script kiddy has the same phone as you and they share the rom they built from source. Hit or miss, sometimes very good, sometimes terrible. Updates stop when script kiddy gets a new phone.
Official 3rd party rom, Lineage is the most common, Crdroid, Graphene, eos and other secure and special roms are in this category, but they support far less devices. Updates are automatic, built by a server every month. Someone have to set it up, so you still need someone interested about this in the community, and the manufacturer have to release drivers, firmware. (They should be legally, but noone cares) Usually that’s the best experience you can get on an Android device nowadays