Thanks. As Goran says above, as far as we can tell this is an issue with Apple's OpenGL implementation on Apple Silicon-based Macs and as such likely only they can resolve it. However, if you are feeling brave, there's 2 workarounds that may alleviate the issue, but if you choose to use them it's entirely at your own risk.
1. If you have a copy of X-Plane 11 installed, copy the DDS files from X-Plane 11/Resources/bitmaps/Earth Orbit Textures to X-Plane 12/Resources/bitmaps/Earth Orbit Textures, overwriting what's already there
2. If you don't, you can resize the DDS textures in X-Plane 12/Resources/bitmaps/Earth Orbit Textures to 1024x1024 pixels (how to do this is an exercise left to the reader)
We still hope that when Gizmo goes "ARM native" (and Rosetta won't be required) it'll bypass whatever OpenGL issue is the cause, but I'm not holding my breath.