How can I use iPhone 11 Pro Max (A2161) in Europe?

Hello,

I live in Europe, but my friend was in the US some weeks ago, and brought me a new iPhone (A2161 model). When I get the phone and tried to activate it, I couldn't do that, because it said that "Not supported sim". I did some research and it turned out, that he bought the phone in the BestBuy, who not sells unlocked devices, just universal iPhones, that can be activated once and then locked to the first carrier. I've contacted with BestBuy, but I didn't get any useful info.

My questions would be the following:

1. Is it possible somehow, to unlock the phone? It is not activated yet.
2. If I order a USA sim card, can I activate the iPhone with it, while I'm in Europe?
3. If I activate the phone with a US T-Mobile SIM card (so then I lock it to this carrier), is there any chance, that it will then work with my Europe T-Mobile SIM card?
4. Do you have any idea, what could be a solution to use this phone outside US?

Thank you in advance!

Best regards, Roland D.