I have went to the Internet in order to find commentaries on doing what I have done and found that there was surprisingly little information about using OneNote with NextCloud (as opposed to OneDrive).

Good search is always appreciated tho.I was motivated to stop using OneDrive to store and sync OneNote between computers 1) in order to “own” my notes utilizing my own NextCloud server 2) To resolve the 5 GB limit for free OneDrive. This space is still missing a nifty solution, a lot of non-technical people also prefer non-MD software for the added freedom, and they are not interested in the whole graph, linked notes thing. WYSIWYG solutions also had their share of problems, like when pasting formatted data that afterwards you just couldn't get rid of. Markdown doesn't fit this scenario very well, even with table plugins in editors. I miss classic Onenote, being able to paste tables, color a few rows here and there, design my timetables and artisanal kanban but keeping it simple. It's decent now, but still far from ideal. So yeah, my current notes workflow is pretty much in Markdown and Obsidian, with the occasional PDF or word document thrown in the same folder for detailed notes or where I need images (gallery plugins don't cut it and I don't want a cluttered file list) Themed the app with the new Border theme, and added some plugins to declutter the UI further, like Hider. I'm yet to try a nextcloud instance with onlyoffice or some note taking tool, and replicate this idea but customize it further. I've tried using google docs and a makeshift sidebar to the files, but there's no instant loading, WYSIWYG is not the same and the overhead of a full word processor shows as it is not a canvas, notes won't load instantly, cross search will take more time.

Right now, not much choice really, and the current zeitgeist is pushing for progress in the markdown/second brain space with Obsidian and similar tools. The writing was on the wall, as that version was too different from the path they were going down with the Windows version. It was one of the few apps that felt it had the right balance, and it looked good on the Mac too. I had the same problem, happily used Onenote 2016 for years but the next version broke too much of the good stuff to stay there, plus added platform lock in as I couldn't really keep my notes local anymore.

Microsoft one note alternative