Apple Mail problems with macOS Ventura

Since updating my MacBook Air (Retina, 13 inch, 2019) to Ventura (13.0.1), I've been having problems with Apple Mail. It often gets stuck with an error message: "Copying messages." See attached image, lower left corner. Then I can't quit the Mail app, and have to Force Quit. Sometimes that fixes it, sometimes not. Sometimes restarting the Mac will fix it, sometimes not.

Anyone know how to fix this problem? Thanks.

Aryae