With the series x there is a new setting to setup hdr for gaming from the console.
For that you need at least HDR10. My tv has HDR10+ and does not work with the setting.
Apparently my tv does not support that my series x says. I tried many things like the official support guide => did not work. Changing settings on my tv and such.
Depends on the TV. For example, LG OLEDs required deepcolor to be turned on at the input level in the settings. Have you checked something like that on your set? Make sure your cables are seated securely on both ends. Also, cables are cheap. Do you have a known good cable that works? Some cables are rated as directional. Make sure those are connected properly.