Is this login screen legitimate?

So a few days ago I received an email from Apple, telling me that my iPad had been removed as a trusted device from 2 factor auth for iCloud because my iPad had been reset, except my iPad hasn't been reset.

I didn't think much of it, but then when I went on my mac the next day I got the following login popup

Now I'm sure I've seen this before, so I put my password in, hit log in and the message shows again, try again, same thing. Hit cancel, it pops up again. Hit cancel a few more times and it finally goes.

So I start to get a bit suspicious, change my password, reboot and the same again. It won't accept my password but doesn't give me an error.

Is this just a really badly made/designed legitimate login screen, or is it malware designed to collect passwords? How would I know? there's nothing that gives me confidence it's anything but malware.

If it's legit, why doesn't it work? why do I have to dismiss it three times every time I boot the machine?

And why did Apple send me that email? (i'm pretty sure it's a legit email judging by the headers, and the fact it went to both my notification email accounts and they knew the name of my iPad)

Given I have 2FA enabled, use reasonable passwords and generally don't login to anything on other peoples networks or install much software, I'm fairly confident this is just stupid software, but it would be nice to be sure about that.