I downloaded the latest Google Camera from APK mirror and turned off all network access in Datura Firewall (comes with CalyxOS). This is a pretty common recommendation on /r/CalyxOS. Another recommendation I've seen and wish I'd done is to extract Google Camera's APK from your stock Android via adb before you flash Calyx, thus avoiding APK mirror.
Only trouble is after you take a picture and tap the thumbnail to view it immediately, it wants to open it in Google Photos and that is apparently not configurable. Simple enough solution - downloaded Google Photos from Aurora and blocked all network access just like Google Camera. Most stuff in Google Photos doesn't work but it's fine for a local gallery viewer.
From what I gather no other camera app will even come close as the Pixel series works closely with the Google Camera app to bring software optimizations to the photos that specific camera module takes.
Only trouble is after you take a picture and tap the thumbnail to view it immediately, it wants to open it in Google Photos and that is apparently not configurable. Simple enough solution - downloaded Google Photos from Aurora and blocked all network access just like Google Camera. Most stuff in Google Photos doesn't work but it's fine for a local gallery viewer.
From what I gather no other camera app will even come close as the Pixel series works closely with the Google Camera app to bring software optimizations to the photos that specific camera module takes.