I have only just recently purchased the TV (23rd March) and received my Xbox Series X last week..
I have issues with running the TV when trying to run 4K @ 120Hz and keep getting Input Signal not detected or Mode not supported (Change Resolution). The home screen works fine on the Xbox it's as soon as it tries loading a game - sometimes the game will display after a few minutes and others it just flickers back and forth with Game mode On / Off.
I have been on Chat support and had one of the visiors remotely login to my TV to reset to factory defaults and refresh my HDMI ports. But this has not helped.. I have found a work around but switching off Game Mode and only turning it back on when the game has actually loaded - this allows me to get 120Hz at 4K and FreeSync with HDR and UHD.
Is there a fix available for this? I am thinking of returning the TV if there is nothing planned to fix this issue.