Task: writing a small multiplayer game. Question: on what to base the server part? What technology to choose?

Question

Computer networks

Explanation: the client part is not interested, the question is only about the server part.
Suppose I have a client for the game (let it be a shooter). This client perfectly renders the area around the player, weapons, sounds and animations of shooting.
Task: how do we now combine the players so that they can shoot at each other? :)
Probably, you can start from scratch, and sit down to read big gamedev forums and books.
But maybe there is something simpler? Some ready-made server engine, for such things as:
1) Maintain connections with 10k of clients
2) Receive status updates from them (where the player is, where he shoots)
3) Calculate who shot whom
4) Notify other clients about the state of the game (who is where, who killed whom)
5) do it with a digestible update rate. Well, let's say 0.5 sec
6) Preferably cheap
7) Non-gluttonous to resources (so as not to go broke on hosting)

Answer 1

“Receive status updates from them (where the player is, where he shoots)”
- Where the player is, the server itself must know, otherwise flying cheaters will appear;)
As a matter of fact, unfortunately, I can’t suggest anything. Haven't come across anything suitable.