For now I have turned DirectWrite off per @Coises’ advice. I had turned DirectWrite on per this thread from April 2023
The video drivers seem to be up to date, or at least Windows Updates, plus “check for updates” at the driver level claim that things are up to date. There was an update for my monitor which I installed.
I suspect it’s something triggered by Notepad++ or Scintilla. If it pops up again I’ll see if the glitch gets cleared by clicking with the mouse, etc. I normally use Alt+Tab to switch applications.
I don’t feel like uninstalling Windows updates per what @Ekopalypse dealt with as the blobs issue has been going on for several months. My first screen shot of one was on February 8th. The blobs don’t happen often and when I notice one they have been “fragile” in that they vanish as I try to do anything.
At least I have been able to capture them using screen shots. That in itself proves they exist and that Windows knows they are on the screen meaning they are not artifacts created the video hardware and/or monitor.
The unrelated missing right parentheses issue was quickly resolved by @donho.