How Photon CCU works?

Hi, i was reading an article on the website of the Photon engine and found a part saying that it was capable of holding up to 100 ccu, which would be the number of simultaneous players, but wanted to know if that number of players would be just one game or at all the game? I thank you for your attention :)

It's complicated. The Photon Server is capable of keeping thousands of connections. But you can not sync each player with everyone else.
By default, Photon puts players into rooms. So many rooms can be run on a single server but each has only a fraction of the players.
Syncing the updates of 100 players is quite complex, as the network bandwidth is usually not sufficient (and you don't want to rely on a high-end network either). So it's more 10 to 20. With some effort more.
There is no out-of-the-box networking solution that allows 100 players or more to be synchronized with one another.

Hi, thanks for replying. So, how multiplayer games are made, like Rust or DayZ; or even small games like Fall Guys? they have many rooms with several players

how multiplayer games are made

Use google to find out.
There are lots of different approaches and it's beyond answering a forum post to answer this in any meaningful way.