Mail - Moving Messages

The perennial problem with Mail, moving messages!

iMac with 11.6.2 Bug Sur. Since late morning today my Mail app has been moving the same 113 messages, being stuck on 1. I have cleared out mail from my ISP (I use IMAP) cleaned up the Mail folders on my Mac

carried a long winded rebuild of said folders and I'm still stuck with the magic number of 113 moving messages.

I can see this problem here many times here, I've had this before but the upgrade to Big Sur killed it, but now it's come back to haunt me.

I have tried all the other suggested solutions re-start in safe mode so on and so on, they do not solve the problem.

Does anyone have a definitive solution to this problem, I find it hard to understand why it continues to occur?