If you're not receiving email at all, this may be an issue with your mail provider. If you post who your provider is, someone may be able to of offer an opinion.
However, if you're getting the emails but when you go to look at them they're blank, that's a long-standing bug in earlier versions of macOS. I have an iMac also running macOS 12.7 (iOS runs on iPhones) and I regularly run into this problem. Quitting Mail and relaunching it fixes it for a while, though sometimes I have to do this a couple of times, and the problem eventually comes back. The bug has been reported to Apple by many and the answer from Apple Engineering was that it was fixed in "a newer version of macOS" which of course doesn't help those of us for whom macOS 12.7 is the last version our systems can run.
If the scenario I described is what you're running into, then I'm afraid that there is no fix if macOS 12.7.x is the latest OS you can run. You'll need to consider a third-party email application.
Regards.