The camera on the pixel is amazing but yeah the grapheneos software for it loses a lot of functionality like panorama, portrait, night mode, etc...
But you can download whatever camera app from whatever app store and it'll run sandboxed.
Discussion
The issue isn't so much the app, but the drivers. Once you dump the OEM ROM, you loose the good stuff that makes the camera so good. That has not been overcome and may never be. I am not yet willing to give up on that yet.