Markdown is typically written in text editors, not document editors, so the fact that Markdown editors in Standard Notes use variable-width fonts is quite confusing to the eye (and uncomfortable for things like e.g. aligning lists items with depth > 1).
It is true that GitHub comments are markdown and use variable-width, but this is meant for small comments, typically smaller and less complex than notes in Standard Notes. Other notes apps like Inkdrop or Joplin use (or at least allow to use) monospaced fonts in Markdown editors.
Please set the markdown editors to use monospace font, or at least allow the option to do that just like what can be done with the "Text" editor.