Which HDMI input are you using? I just bought the Q80T (and now getting a replacement from Amazon due to dark spots...) but I read on Rtings.com that it supports 4k @ 120Hz on HDMI 4 only. I'm waiting on my PS5 to get delivered Saturday or Monday so I'm curious what your results will be.
I have the exact same problem, but with series x, so would also love an answer. Series X show it supports it in its video modes screens, but when starting any game, it does not start in hdr.
Mine works for series x when I played the new soccer game (feefa 21). I saw it show VRR, 120 HZ, UHD, and HDR on the display info when you click the center button on the remote.
I have the same issue. HDR @ 60hz works fine but at 120hz it turns it self off and cant be turned on again until i switch back to 60hz. Hopefully Samsung fixes this sooner rather than later.