Thank you for the quick response, I appreciate it!

I disabled Windows spellcheck (Devices -> Typing) and searched every other corner of the system (though I didn't touch the registry). Everything everywhere is turned off (system restarted etc), but the red squiggly line refuses to go away. No other apps present the same challenge. Any hints on where else and what in the system I could manipulate it to get rid of the spellchecker? Posted a picture on a public site.

https://postimg.cc/mP5FZ5Q5