What application uses the rstf://scheduleState=1 URL scheme?
You can use the RCDefaultApp preference pane to see a list of all URL schemes provided by applications on your system.

These supported URL schemes are defined in the Info.plist of an app, and registered collectively by macOS.

Sadly, I do not have any apps installed that handle rstf:// but please let us know when you find out what it is!