Apple Mail Running Amuk

I have a new 14-inch MackBook Pro; Montery, version 22.1 I hired a private apple tech to move information from an older MBP to the MBP. I didn't want to use migration because of some problems on the old MBP

I use Apple Mail. After a few weeks using the new MBP emails began acting strange, including disappearing. Emails in I-map mail boxes seem to still be there. Email that was not processed and still in the inboxes disappeared Also , deleted emails come back to the Mac; The "Sent" mail box is empty no matter how many emails I send; Drafts does not work; This is a business computer and some of the losses were important. I hope that I will be able to retrieve the lost emails from either BackBlaze or RackSpace. The old computer that was used to transfer to the new also also lost the same emails. I do have Apple Care but I'm not sure what good that will be. I had to think virus but that has never happened to me. Clean my Mac says I do not have malware. I am hoping to get suggestions from the Community. Steve