I can understand there would be a use for this, but as there are other ways to do it it’s relatively low priority in my list. I wouldn’t be opposed to a pull request for it though.
Yes if you want more security, the best way is indeed to use something like Truecrypt (that’s what I use for my notes or emails for instance). It would also prevent access to your data if your laptop is stolen for example.
If what you’re interested in is simply to hide the application from other users of your computer, and you’re not worry they’ll dig in the folders to find your data, there are various tricks you can use - https://www.online-tech-tips.com/computer-tips/hide-windows-desktop-screen/