It wants a username and pw but I don’t what it is
Pretty sure there’s a setting that makes you type the username in instead of clicking on it, for a little added security
I’ve only ever seen this when our company MDM didn’t play nicely with a macOS update, did you buy this computer used?
The others
This Mac was previously domain-joined. When buying a used computer (in person), look out for previously company-owned computers as this one could have been stolen, or given to the pawn shop by a former employee illegally. You would most likely have to take it to the company it originated from (prior to the pawn shop) and ask them to remove it from the domain. Although, they may refuse.
Never buy used I would say. I won’t even buy refurbished from the Apple Store
I’m sorry but this is the most dog water take I’ve ever seen. Firstly, what to you suggest happen to used MacBooks? Send them off to a pile of burning electronics for kids to sift through for precious metals like other e-waste? These machines last 7-8 years with official support, and the ones prior to 2015 have user changeable components and can easily run more supported OS’s like linux. There’s absolutely nothing wrong with buying used mac’s so long as they’re not enterprise or iCloud locked.