That was not my intention but given the progress within a work day (I spent some of my weekend on this) it might be more reasonable to just rewrite Nextcloud Notes for iOS from scratch with SwiftUI, SwiftData, EasyMDE in WKWebView and so on. There would definitely be major advantages. From user perspective to developer work.
I mean, I did not get to ask myself "How would I do it, if I could start over?" for no reason.