I'm the same, not bothered about 120hz really, 60hz with better graphics is my preference. Despite that I do have my series x in pc mode with 120hz enabled on the series x.Hard to say. 4k 120hz is pretty much bleeding edge and a lot of TVs which support it were released before devices which used it actually existed. There are known issues on LG OLEDs for example which LG need to fix. Similarly the Xbox is pretty new and I wouldn’t be surprised if it required a few firmware fixes to get it running as stable at it can be. I’m just going to ignore 120hz on my LG C9 for the time being. I can’t actually imagine me playing games at 120hz anyway as my preference would be to suck at 60hz and get the extra graphics bells and whistles.
Are you using 60hz then and in pc mode?