I used to just use a cloud service like you years ago, but try sync them through GitHub, there is a 1gb limit on private repositories though, but it should be fine as long as you don’t put videos and sounds in there.

https://www.youtube.com/watch?v=Cu4-BPcveBI

There are tons of alternative ways for you to sync notes. I have used it for so long without spending a dime.

Oops, I didn’t even notice.

Man, you left out Obsidian, it is a godsend for studying and notetaking.

Get an ultra-wide monitor, split it into four panes, one pane to import the pdf you want to read, another for note-taking, and spare another one for the AI for Markdown formatting and explaining texts (optional). I can’t think of a more efficient workflow for studying digitally.