Take some time and really analyze your threat model. There are different solutions for each of them. For example, protecting against a friend swiping the drives may be as simple as LUKS on the drive and a USB key with the unlock keys. Another poster suggested leaving the backup computer wide open but encrypting the files that you back up with symmetric or asymmetric, based on your needs. If you’re hiding it from the government, check your local laws. You may be guilty until proven innocent in which case you need “plausible deniability” of what’s on the drive. That’s a different solution. Are you dealing with a well funded nation-state adversary? Maybe keying in the password isn’t such a bad idea.
I’m using LUKS with mandos on a raspberry PI. I back up to a Pi at a friend’s house over TailScale where the disk is wide open, but Duplicity will encrypt the backup file. My threat model is a run of the mill thief swiping the computers and script kiddies hacking in.