Out of the box, the Sony X950H is really not set up well for your Xbox. When you check 'General 4K TV details' in settings, you might be disappointed to see barely any green checkmarks, and a whole bunch of 'Your TV does not support (some feature), even though it totally does. It's not super intuitive to get them to work though. So here's what you need to do.
Hit the Settings button on your remote (gear icon).
Go left on the on screen menu and scroll left to 'Settings'
Click 'Watching TV'
Click 'External inputs'
Click 'HDMI signal format'
Click whatever input your Xbox is connected to and make sure it's set to 'Enhanced format'
That's it! Such a crucial feature, buried in all those menu options. One other thing you might want to do if you don't get the HDR recognition on the 4K TV details status on the Xbox, is:
Hit the Settings button on your remote (gear icon).
Go to 'Picture settings'
Make sure you're set to Picture mode>Gaming
Scroll all the way to the bottom of the picture menus to 'Video signal' and set HDR mode to 'HDR10' from Auto.
If your Xbox status already gave you the HDR green checkmarks, then there's no need to manually set this to HDR10 from Auto. Just a troubleshooting step for you in case. Your Xbox settings themselves should already be set to enable all the features your TV supports, so there's not much there to change.
This is what you should see when you've got everything correctly set up:
For some walkthroughs on other TV's (not specifically the X950H), check this article out:
Happy gaming!
Followed all your steps but cannot get 4K at 120Hz. Only at 4K 60Hz.