I know I could and should encrypt whole drives but I want another layer of protect specific folders when my devices are unlocked, a password. I want the folders to behave like regular folders where I can add or remove files as usual, without a clunky UX like password protected zips. I looked it up and didn't find any straightforward solutions.
I don't think you can do this without encryption that all 3 OSes can recognize, which will lead you to password protected zips.
Edit: Apparently there are some solutions.