like u said notes are really personal. I personally prefer paper the most, but if its about electronic notes, I settled with a folder that gets synced with syncthing to all devices and also got git for easy offsite backups with push. (yeah, syncthing does that too, but I like to have a history in my backups, to allow for single file and state restores)

In this folder I categorise with subfolders and use simple markdown files to write down stuff and todo.txt for when I need tasklists. A dedicated file in root is used for collecting random stuff before there get sorted and another to collect all links that I wanna bookmark.

This works very well on different types of devices at the same time. On android Markor is a good editor for it, on desktop/macs I recommend typora for the nice interface and obsidian.md for the nice navigation between files, if you don't have already have setup a favourite editor. Also works well with vim/emacs/vscode or anything else that handles plain text files.