As others have suggested, it varies, but in my experience, knowing my full name, room number, possessing a key and knowing how I paid for the room has always been enough. Last four digits of the card used for the room tend to seal the deal in every case, but were not acceptable for MGM (despite me having that very card on my Apple Watch).

In the UK, at least, it's unusual to show a driver's license for anything (except buying alcohol if you look young) because many drivers don't carry them, whereas in the US I had to show it every time I even checked into a hotel and even occasionally when buying things with a credit card.

In Europe? Don't you mean "in that specific hotel, on that specific day, with that specific employee"? Do you really think everyone follows the rules to the letter when they're making front desk wages? That job is 100% replaceable.

Sometimes workers get tired of dealing with persistent people who absolutely insist that they are correct (which in this case they were), and realize that they don't get paid analyst wages, they get paid front desk wages, and they say "Okay, this looks right to me. Here you go."

They do yes, some bastards even want to hold on to it which is illegal in all of Europe.