Your knowledge of the underbelly of Joplin is simply amazing! I'm sure if you ran into my problem, you would be able to fix it quickly.
I'm different. I came to Joplin from Evernote. I used Evernote to keep my notes and just used the program for my needs and that is all. I had no desire or time to learn all the fancy extra things you could do with Evernote, as I didn't need them.
It's the same when I came to Joplin. I just use Joplin to keep my notes which keeps me organized to do the other things that I need to do in my life. I just use the easy WYSIWYG editor. I've never used the markdown editor. While interesting, I don't have the time to get the incredible knowledge you have for Joplin. I just want to use it. Another problem with using markdown is my lack of knowledge of this programming - I've looked at the 2 lines (starting with "$\sigma =") and can't see any difference in the 2 lines. UPDATE: In looking at the KaTeX error you made and it saying the problem is position 16, I finally saw you added an extra "c" in the "\sqrt" area. Is that how you generated the error?
I'm still going to study what you wrote in this reply to see if there's something I can do to fix what I have now, and if I will be able to trust Joplin again. I'd love to get my data back. If I'm going to be able to use Joplin and trust it, it looks like I need to learn how to use markdown. Perhaps there are some articles or videos regarding my issue (and perhaps how to use markdown), but I haven't found any good ones yet. But I have hope. I really like Joplin and the community and want to stay here.
Again, thank you for your generous assistance!