Yet another victory over MacOS!

To stop MacOS from rearranging your virtual desktops (after you have them just the way you want them):

Go to System Preferences > Mission Control
Uncheck “Automatically rearrange Spaces based on most recent use”

Thanks to:
https://www.appsntips.com/learn/how-to-stop-mac-spaces-from-rearranging-themselves-on-macos/

P.S. If virtual desktops (or “Spaces” as Apple calls them) are new to you:

Press “F3” to view your virtual desktops.

You can have multiple Spaces to group related windows and then swipe left & right between them using 3 fingers on your trackpad or magic mouse.