As far as I understand this needs to be implemented into every service individually, so as long as providers like Disney+, AppleTV, etc. If the providers don’t bother, I as an consumer cannot use FCast, right? Or can it act as a drop in replacement for Chromecast?
If it’s just the ntfy app that sends these alerts it should be easy enough to send the developers of that app a feature request to implement a sleep mode which can be scheduled to mute the notifications.