No, this is my personal device. It has never been connected to any MDM.
Have you actually checked your device management settings?
Yes. In Settings > General > VPN & Device Management, it says 'Sign in to Work or School Account'. Is there a different device management setting that I should be looking at?
That's the one. I was worried you might have something you didn't know about!
Yes, there are alt app stores that try to get you to agree to installing a MDM