Knock on wood, but it LOOKS like the latest AMD graphics drivers (Adrenalin 23.2.1 (WHQL) dated 2/14/2023) have fixed this issue. I downloaded and installed them (w/ the factory reset option selected) and tested Calibre by repeatedly editing a book and then closing the editor ("T" | ALT-F4). I did that a couple of dozen time without problem. I also did the same with the Viewer ("V" | ALT-F4). Similarly, no problem. Here's hoping that continues.
My assumption was AMD's handing of the OpenGL stuff that QT WebEngine uses (that Calibre uses that lay in the house that Jack built
) was not up-to-snuff. There's nothing in AMD's Release Notes specifically about OpenGL fixes. But, regardless, I'll take whatever the fix was.