What Happened to the AirPlay Option in Quicktime?

I've been using Quicktime for years. Simply clicking on the desired file, then when the file opens there is an AirPlay option. Not anymore. It's just like it always was but no AirPlay option. Mirroring the screen is no problem, but then I can't use the computer while the movie is being played. I've gone through the rebooting process (which seems to be more and more a common aspect of using the Apple system) but it remains the same, no AirPlay option. In "Help" AirPlay isn't recognized. I've used it this way for many years, never a problem before.