Well, yeah.. you never want to test backups on the same computer you made them, so to test them, you should go to secondary/friends/work computer and try to access the files. Boot from a fresh LiveUSB stick if you are feeling paranoid. At least once you have backup configured, there is often a fuse driver, so an easy way to do so is to browse backups and try to open a few documents at random.

As for "encrypting your backups", that's what the "check" command is for - it can't ensure that this .py file actually contains python code (and not encrypted data with ransomware message), but it can check that indices are well-formed, and file checksums match the uploaded contents. Obviously it should also be run on trusted machine.

Not sure what this whole "blockchain" comment was about.