FWIW, Joplin allows you to have a single panel "raw markdown" view, and you can just assume it'll all render the way you want, and maybe double check at the end. I find that works well for me. As you say, previewing what bold looks like offers minimal value. :)

Joplin also has a beta single pane WYSIWG view which is like, I believe, Typora or Bear (markdown in the backend, but you type in what is effectively the preview window). I haven't really tried it out yet though. If it works well though, it might solve your concern though.