Here you go:
Issue: “mail has no content”
This is not the easiest fix but the only one that worked for me (should work for either Monterey or Ventura):
After trying every suggestion, I finally (as a last resort) booted into recovery, erased my drive and reinstalled the OS (Monterey, 12.6.3). I then migrated my files, apps, etc. from my TM backup. This fixed the mail issue. I tested this for the last 7 days (150 emails) and the mail is rock solid. I’m guessing somewhere along the way after some OS security update the issue started.
NOTE: Before reinstalling the OS I tried updating to Ventura but the issue continued. I also tried just reinstalling the OS not touching the data volume but that did not work. I had to erase the drive and start over.