I have Cryptomator setup with a single vault, created using iOS and located on iCloud which means that it is inside the Vaults subdirectory. When I open the vault (named Private) in the iOS Cryptomator app I can view work with the file as expected.
If I launch iOS Files app (NOT the Cryptomator app) with Cryptomator turned on as a Location and then in the Browse Locations view tap on Cryptomator I get a very quick window opening and then it disappears so I see the Browse Locations again.
On an iPhone this looks like a blinking screen, but on iPad the pop-up is not full screen so I can see the pop-up view very quickly with a spinning progress circle and then it disappears.
This appears to be an incompatibility with the current Cryptomator build and the current iOS build including the Files app or Files Locations support isn’t really implemented yet…
I was excited about Cryptomator showing up as a Location option so that is the first thing I tried after setting up a vault.