My Apple TV Show black screen when i do Screen Mirroring using My IPhone XS Max

Mirror your iPhone, iPad, or iPod touch

Use Screen Mirroring to see the entire screen of your iOS device on your Apple TV.

1. On your iOS device, open Control Center and tap Screen Mirroring.
2. Select your Apple TV from the list. If you don’t see your Apple TV, make sure that your iOS device is connected to the same Wi-Fi network as your Apple TV. Need help?
3. If an AirPlay passcode appears on your TV screen, enter the passcode on your iOS device.

Your TV uses your iOS device's screen orientation and aspect ratio. To fill your TV screen with the mirrored iOS device screen, change your TV's aspect ratio or zoom settings.

To stop mirroring your iOS device, open Control Center, tap Screen Mirroring, then tap Stop Mirroring. Or press the Menu button on your Apple TV remote.

If you still have the same issue, then you will want to take a look at this article for troubleshooting:
If you can't use AirPlay or mirror your device's screen

I have the same problem - Screen mirroring does not work with Apple TV2 and iPhone XS Max. I took my Apple TV and my iPhone to Apple store. I was able to set it up to demonstrate them the problem to Apple store employees. The guys were very patient with me, and spent more than 3 hours on this problem. We checked it out with 5 iPhone XS Max - 2 brand new out of the box, one mine, two Apple store employees personal phones. My phone was tried out with all data wiped out and brought to factory conditions. Of course the brand new phone out of the box did not have any data.

Here is the outcome:

Apple TV2 - XS Max does not work for Airplay and Screen Mirroring - the level of functionality depends on the OS level.

iOS 12.0 and 12.0.1 - Both airplay and Screen Mirroring does not work - Airplay could work sometime - but often does not

iOS 12.1 - Airplay will work reliably - Screen Mirroring will work only in Landscape mode and not in portrait mode.

iOS 12.1.1 (beta) - Both Airplay and Screen Mirroring works properly

With Apple TV 4 - it works with iOS12.1 and (maybe) with iOS12.0

Looks like Apple is forcing people to upgrade their Apple TV. In my case I certainly will not upgrade Apple TV - which does not have all the Apps (Amazon Prime, Sling, DirectTV now and few others), so its useless. Only reason I use Apple TV is for screen mirroring. I am pretty happy with Roku and Fire Stick for all my need. I guess I need to learn to live without it, or use screen mirroring with iPads and older phones.

For now it seems like the issue may be fixed in 12.1.1 - since its beta we do not know what will happen when the iOS update is released.