Also what is the difference between a system tray and a control center?

Functionally, there isn't one. Both serve the same ultimate purpose: To be an area where background services and system functionality can be accessed quickly and easily, while staying out of the way of whatever you're doing in the foreground.

The tray is just an older, arguably more primitive metaphor for the same thing: "Just give every service and app its own icon, and make it so that icon can be clicked to access its options and features". It's simple, but it works.

The control center is more elegant, like, really, it is. It saves screen real estate and such. Giving you a little scrollable window where every controllable thing has its own little area. But that is contingent on the application itself implementing that functionality. When an application expects an old-fashioned tray, Gnome's control center just tells that app to go $&#* itself, when they could, if they wanted to, just add a corner on the control center for "legacy apps". But they don't wanna, because they think they know better than everyone else.