I intend to backup my whole system, secondary and external HDDs to Amazon Cloud. Currently my drives are not encrypted at all. I'm running Windows 10 (no UEFI).

I was wondering what is the best way to securely encrypt private data before uploading it to Amazon's cloud? I would like to have on the fly encryption, so there would be no need to create a container any sync it manually with Amazon's cloud software afterwards, but rather sync and encrypt the whole drive in real-time.

Quite some people recommend Boxcryptor, but it doesn't support Amazon's Cloud. Cryptomator seems like a good choice, but how secure is it, since it's not open source? There is also Duplicati, SyncBackPro and StableBit, do you have any experience with any? How do they compare? Any other recommendations?