Multiplayer server cloud

I am searching for tools to create a multiplayer game.

My idea is to create an android client/server(cloud) game.
I need that when a player do an action, other players are synchronized and receive a notification.
The game should manage simultaneously different match. For example 100 match with each 5 players (so 500 players grouped in 100 match).
Every player can do actions also if others players are offline and when they would open the game they should receive the update of other players actions.

I found a lot of example of Netcode but I am not sure if this tool allow me to manage what I want to do.
Basically I found examples that show how to manage object synchronization but not how manage the connection to a remote server and not how to manage different match.

Can someone suggest me the corret way and, may be, some example/documetation?

You may want to simply run through all the examples and tutorials to get a feeling for how NGO works (other solutions are not much different).

This will answer some of your questions. Most importantly there is no concept of a „match“. These are either separate instances of the server, or the server handles all connections and divides them up into matches (not recommended since you cannot easily limit data transfer to just a subset of connected clients, it will at least be awkward and error prone to implement).

You should also look into Unity Gaming Services, specifically Relay, Lobby, Matchmaking.

You have a lot to learn. Like serious amounts based on your questions I would say if you are an experienced developer just without network experience you are looking into 1-2 weeks fulltime research. That shouldn‘t stop you of course, just setting expectations. ;)

Thanks. Of course I have to learn, but I am not scared. Thanks for your indications