He should definitely file his 2023 return on time.
If he has not already, he should set up an account at the IRS website and he can find out the status of his 2022 return and previous years also. That will be valuable to know, so he knows how to go about rectifying it, and he'll now if anything has been done about it there.
I could not e-file, had to physically mail it, had no choice. I only found out through my IRS account recently when the status went from pending-meaning it had been received-to absolutely nothing at all. No status available.
This is not tax advice. This is dealing with bureaucrat and bureaucracy advice. Good luck to him.