There's DroidFS. It allows you to mount gocryptfs and CryFS-encrypted volumes, which work closs-platform with desktop operating systems. Unlike Cryptomator, it's also free. Note, however, that gocryptfs does not obfuscate file sizes, while CryFS can. Depending on your threat model, that may or may not be necessary. If you have to go the CryFS route, it's probably best to take a step away from your phone and brew a cup of coffee while moving files to/from the volume, as it's very slow lol.
Cryptomator also doesn't obfuscate file sizes.
DeletedUser232
It works if you're attaching small files in KeePassDX, but if you're trying to attach files that are over, say, 512 MiB, it's very likely to crash before it's done attaching. At least, that's my experience.