Connect your Mac and Xfinity Streaming Box to the same Wi-Fi network
Open Control Center on your Mac
Click Screen Mirroring
Select your Xfinity Streaming Box if it appears
Enter the AirPlay code on your Mac if prompted
Open the app or content you want to share
If Screen Mirroring does not appear, check whether your Xfinity box supports AirPlay
Update your Mac and Xfinity box software
Restart your Mac, Xfinity box, and Wi-Fi router
Use an HDMI adapter or Apple TV if AirPlay is not supported