This app was mentioned in 7 comments, with an average of 1.14 upvotes
Hmmm.... well, this isn't an unknown app. Just a little less known...
Boxcryptor On the fly cloud file encryption and decryption (Dropbox, GDrive, Box, etc).
I think an app like Boxcryptor - https://play.google.com/store/apps/details?id=com.boxcryptor2.android OR Cryptomator can be used to encrypt prior to manually transferring to your cloud storage provider of choice.
There sure is...
Boxcryptor: play.google.com/details?id=com.boxcryptor
It encrypts local and various cloud services. It's not exactly free, but it's the most advanced local/cloud file encryption software I've found for android.
Here is the technical overview: boxcryptor.com/technical-overview/
Once you set up your account, you have the ability to export your private key, which you can use with VERACRYPT on your PC/Server.
Hope this helps!
Try Boxcryptor. https://play.google.com/store/apps/details?id=com.boxcryptor2.android
Edit: it's not a Cryptomator client. But works the same. And it's trustworthy.
Do you know/have any thoughts on boxcryptor