Your Pixel's auto-rotate isn't broken. You just haven't turned on the right one. Buried in your Android display settings is a second auto-rotate mode that uses your Pixel's front-facing camera to ...
The Google Phone app now supports landscape UI, meaning it will rotate if your system-wide auto-rotate is on. However, this feature apparently keeps getting added and removed between stable updates.
Your Pixel phone is loaded with excellent software features. These 6 are ones you probably aren't using — but 100% should be.