This image has both JP stack exchange and meta. Meta displays normally, but the main site became 3D
This image it's just wrong:
Maybe this is due to dark mode in stackoverflow?
Yes, it does appear to be a bug in Stack Overflow's dark mode, as you suggest:
In fact, there is already a post on this topic over on Meta Stack Overflow:
https://meta.stackoverflow.com/questions/397173/wrong-icon-showing-up-in-inbox
An employee has already responded over there, and it's currently status-review, so hopefully it'll get sorted out soon :-)