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.
There aren't any to my knowledge.
All 3 OS's would have to expose some kind of facility that makes this straightforward. But not even FUSE is easily usable across all the platforms.