Not a custom ROM maker, though I did get lost trying to plan one for my old Xiaomi Mi A3 (laurel_sprout). Another guy did make a unofficial LOS for it though.

Not a custom ROM maker, though I did get lost trying to plan one for my old Xiaomi Mi A3 (laurel_sprout). Another guy did make a unofficial LOS for it though. Custom ROMs nowadays require you to be scouring Qualcomm out of tree source repositories (or firmware dumps of equivalent phones, I think, in the case of Mediatek). It's impossible to guarantee quality with this conditions. Even if you just want to have a pristine kernel tree of the original firmware you may find, if it was ever released, it was squashed on the wrong source commit (again, laurel_sprout, though a random Github angel fixed it). So Google's devices tend, thankfully, to have better sources. Additionally, GOS team is competent and, for now, sustained full-time by donations. Those three conditions are what allow GOS to be a very good ROM. Do note: it has its quirks, specially with the new trimestral code dumps by Google where half-baked features are on the source (though disabled by feature flags).