A long time ago, there used to be software which would password-protect individual folders.
The downside was when you needed to scan disk, it would have no access to it as I remember.
I backup my stuff onto an external drive that I connected to a ON/OFF switch power extension cord. So I have to press the button to turn on power, to enable access. It's physically impossible for anyone to get to it, other than in the brief period of my backing up files to it.