Encrypting backups with Time Machine

Even though it is actively encrypting, encryption does not prevent or otherwise interfere with Time Machine from doing everything it does without encryption. All backups created subsequent to enabling encryption are encrypted.

It's working the way it's supposed to work. Let it.

Consumer grade HDDs are all pretty much the same cheap disposable junk. All the more reason to have a few, so that if one fails you can just throw it out. The added bonus of using encryption is that it obviates any concern about being able to extract its contents, which remains a glaring security vulnerability.

From Keep your Time Machine backup disk for Mac secure - Apple Support:

• If you back up to an external disk and don’t use disk encryption, any person who gains possession of that disk can read any data backed up to that disk. Be sure to physically safeguard your backup disk so untrusted users don’t have access to it, and store it in a secure location.

I naively thought it would keep or prompt for the setting. Time Machine then gives me the unencrypted warning, so I decide to set it to encrypt backups in the control panel.

Apple ought to enable encryption by default instead of the other way 'round, so that you wouldn't have wasted the time finding out. I would like to think the reason is that they're preparing TM to back up to APFS formatted volumes, but I have no direct knowledge of that.

So between 1 and 3.5 days to go.

That's about right.

I found this cute little script you can use to extrapolate its completion:

https://gist.github.com/lukasbesch/d579c5670ea81d1064cc8f3d5e796a9d