The Google Camera 8.1 update is limiting the use of its astrophotography feature. For devices like the Pixel 5 and Pixel 4a 5G, these will lose the ultra-wide astrophotography support, which uses the ultra-wide lens. If you still want to use that sensor, it works with regular Night Sight photos (Night mode for other devices). Your Pixel will prompt you to "Zoom to 1x for astrophotography" before you can enter that mode.
Astrophotography works to help you take photos of the night sky when it's incredibly dark. You'll need to prop up your Pixel to get it to work. It isn't clear why Google introduced this change in November, but it might have something to do with overall image quality.
Source: 9to5Google