I’m currently on a niche Vanilla Custom ROM. My device is fairly new (came out in the end of 2021 or the beginning of 2022, I bought it in the first half of 2022) and is quite niche (mid-range Xiaomi device). As such, it doesn’t have proper official support for many ROMs, but some people on a Telegram channel have gathered together to build Custom ROMs for this device. I have MicroG but don’t use it because I haven’t configured it properly. If LineageOS for MicroG ever becomes available for it, I would switch to that, so I have MicroG properly configured. The thing is, the people there don’t care about privacy, they are tinkerers only.