In what form and where is the data about installed applications stored (in Google FireBase)?

Question

firebase

For the first time I built a mobile application on Ionic5 + Cordova. Enabled sending push notifications via Firebase using the cordova-plugin-firebase plugin. Notifications come, everything is ok.
But I can’t understand where the data on the number of recipients (installed applications) comes from in the Cloud Messaging console i.imgur.com/5sv0Ve8.png The Database section of the console is empty, I didn’t find any other storage locations. Or did I misunderstand something? How it works?