DoidFS can use the camera to take photos and record video. It gets stored in the vault instead of your camera roll. This ensures that other apps never get access to the photo/video, even if they have "all-files access".
Several other apps does some version of this. If you have tried to export a photo from Signal to your camera roll, you have probably seen this before.
DroidFS does not ask for camera permission unless you try to use this feature. The app does not need the camera for anything else, so if you don't allow it to use the camera everything else still works.
As long as you don't mess around with the "Unsafe Features" in the settings it's very private.