It doesn’t, it just delegates the responsibility to something else, namely xdg-desktop-portal and/or your compositor. The main issue with global hotkeys is that applications can’t usually set them, e.g. Discord push-to-talk, rather the compositor has to set them and the application needs to communicate with the compositor. This is fundamentally different from how it worked with X11 so naturally adoption is slow.
These things are specifically not defined by the protocol. They could be. They’re not, by design.