Desktop: Qownnotes and/or vim (or any texteditor of choice)
Mobile: Nextcloud Notes
Main advantage of this software stack over other solutions like joplin is the handling of the notes. Everthing is stored in a simple folder structure in plain markdown text files (*.md). This means if anything breaks, you are always able to read and edit with any text editor on any system! I switched away from joplin because it stores the notes in a database and notes file names are a cryptic string, so if you are not able to load joplin it’s very hard to find anything.