Contents of Mail Don't Display

I have searched the support community for about 30 minutes and have found questions related to this topic going back 10 years. I have tried many of the suggestions but nothing has worked. I never had the issue up until about five months ago. I will launch Mail and it will display messages in INBOX. If I click on the most recent it will display content of mail. If I click on the next mail it may or may display content. Clicking on other messages will result in no content being displayed unless I quit and relaunch. A thread of messages will show the headers but no content. I have a Shaw account and Gmail account. When I use Webmail to view my messages I can see all in the inbox. I always keep my Webmail clean and at any given time will have maybe 20 messages. On my iMac I always archive emails after a month (both INBOX and SENT) and at any given time my INBOX will only have about 50 messages. My current archive has about 2000 messages. Some of the articles say to Rebuild Mailboxes which I understand deletes all mail on iMac and redownloads from server; but what if they aren't on the server? This issue only started with Monterey. I have iMac 2017 with 16GB RAM. There has to be a fix to this problem. I have run EtreCheckPro and it has found only a few minor issues....not related to mail that I can see.