LineageOS is currently installed on 1.5 million Android devices

https://lemmy.world/post/8595450

LineageOS is currently installed on 1.5 million Android devices - Lemmy.World

For the needs of "degoogled but fully functional Android OS" these days at the end of 2023, the options are LineageOS for most phones, GrapheneOS on a Pixel, and that's it? Or are there more projects at this point?
/e/OS and many others. Look up your model on xda-developers.com, where most ROMs are published. The most commonly supported devices are Google Pixels because AOSP is officially developed by Google for them.
DivestOS divestos.org same developer for Mull browser
Home - DivestOS Mobile

Mull or Mulch?
Both divestos.org/pages/our_apps Mull is based on Firefox and Mulch is based on Chromium
Our Apps - DivestOS Mobile

iodeOS, calyxOS, /e/OS are all good projects. divestOS are also good, but probably not usable for most, because of the lack of google play alternative.

paranoid android seems to still be a thing. The introduction on the website is sparse, and I havent tried it. So I cannot speak for how good it is.

DivestOS added optional support for unprivileged microG fairly recently, so its definitely usable.
Calyx is great. It comes with microG baked in. Also it’s got a great installer. Note that you can opt to keep the bootloader unlocked if you want to root it.
Most phones from one year back, yes. If you want something from 2023 it better be an FP5 or a Pixel

LMOdroid

Similar to Lineage but a few extras. I've been enjoying it a lot. Also seems to have better compatibility with gapps if you choose to install them. Been running Nikgapps full no issue where on lineage pixel launcher would crash frequently.

LibreMobileOS

Rich Featured Privacy Focused Mobile OS