Hey!
I am complained the screen burn-in issue with my nothing phone 3a and I get replacement today, and the thing is I find the same issue in this replaced device also, I think this is not the screen burn-in issue this is a software bug or glitch something else, the temporary screen burn-in issue came after the last software update so you (nothing) have to release a proper software update against the screen burn-in issue.
If anyone facing the same issue please report it.
I hope it will be resolved soon 🙂.