Series X on an LG C1, the C1 has a game mode that gives the VRR info and I'm simply sharing the info the TV is giving me. It also suggests it's playing in Dolby Vision that I wasn't aware the game had???
I'm glad you weighed in with that PooSplatt, because it made me realize one aspect of the numbers you posted that I missed earlier. The figures you posted was 3840 x 2160p@120. When I first read that, my brain said 120 FPS, but now that I read it's your LG C1 reporting that figure, I'd say that 120 is hertz, not FPS. LOL... you made me go check my TCL Series 6 display and I get a res and refresh rate shown there. My TCL Series 6 is a 2018 vintage and it's limited to 60 Hz. It shows 4K at 60 Hz in both Performance and Quality mode. I can say with certainty that the slide show I'm watching in Quality mode with this game is 30 FPS, at best. Also, my TCL also shows Dolby Vision on the display info panel for this game.
I watched a You Tube video of a frame rate test being performed on a Series X running PGA TOUR 2K23 in Quality mode, using analytical software. The game locks the frame rate at 30 FPS in Quality mode, and struggles to maintain even that at times.