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.
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. it now works with unprivileged microg. However use of microg is still is unsupported and unrecommended according to the website.
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.
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.
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.