Hey, just following up. I bought a Cable Matters cable (16ft active powered HDMI 2.1) . I also joined the Xbox Insiders, there was a minor xbox os update which doesn't mention any change on how they handle VRR.

Everything seems to be working, flicker free, with every video setting toggled on in the Xbox @ 120Hz. I'm not sure if it's thanks to the xbox update, the cable, or a combination of both but I tried playing for 30min in the Halo 2 mission that was flickering the most (called Regret, in case you want to try it) and couldn't get it to flicker at all.

Now I'm trying to figure out a ghosting issue that so far has only happened while an object is moving over dark grey backgrounds. Have you experienced anything like that? Here's a video