Many thanks to @PeterJones and @Coises, for the answers, perspective, and (in Peter’s case) updating the User Manual.

You are right, it was Cascadia Code; changing it to Consolas, for example, got rid of it. My “exhaustive” font testing was… only Cascadia Code and Fira Code, so I literally hit both of the two. I’ve been mostly using Hack font for such a long time, I just haven’t really noticed any of this ligature-supporting fonts. I just got a new PC and hadn’t installed Hack yet.

I like finding out where I was ignorant and wrong. It makes me less so.

Cheers and thanks again!
–BrBill