I’m 99% sure they ripped the note editing functionality from Standard Notes.

Not sure to understand, how could anyone 'rip' a note editing feature? Put text in a file (hopefully encrypted since it's online) is kinda the purpose of all note-taking app... which they all copied from their analog (and much older) version pen + paper. And the vast majority of them do it using Markdown, too. Even sync is available in most note-taking apps (with or without E2EE encryption), or do you have something a little more specific in mind they would have ripped?

and try to sell them back to you with a yearly license, even if you host your own server.

That's one (other) reason I like filen: lifetime plans are available (the most interesting ones are offered for a limited-time once a year during blackfriday). No sub.