The internal editor in Framer X is fine, but sometimes it's buggy and sluggish. You can change it to use an external editor from the menu:
View => Editor => External.
Pro tip: Using an external editor is a big time saver when you want to work on the code and see the design canvas at the same time.
VSCode is great but what if you want to use Atom, Vim, Emacs etc.? Answer: