Uhh....no.I know for a Pixel 3a, you cannot even boot AOSP without compiling in the driver binaries:
https://source.android.com/setup/build/downloading#downloadi...
https://developers.google.com/android/drivers
And there is an entire vendor partition (On the Pixel 3a, it was >400 MB). However, even if a user built AOSP with those drivers, VoLTE, SMS on LTE, Wi-Fi Calling, eSIM, and a few other things do not work.
To get those features, one has to extract them from a stock image:
https://wiki.lineageos.org/extracting_blobs_from_zips
I can't imagine this is any better for newer Pixel phones, nor for any non-pixel phones. This will be true for compiling AOSP or any Android ROM.
On top of which, that Pixel 3a is effectively frozen at the kernel it has when it reaches EoL