Update 03/04/2022: Sony released an update to include the full VRR support with firmware PKG6.1576.0180NAA. Past firmware versions like PKG6.1288.0155NAA included VRR support, but Sony said it wasn't the final firmware version, so you have to update it to this latest firmware to get the proper VRR support.
The Sony X900H has VRR support once you update it to the latest firmware. It's G-SYNC compatible as it works with an NVIDIA RTX 3060 graphics card without any screen tearing, including 4k @ 120Hz games. There aren't any of the flicker issues that the Sony X90J has either. 1080p and 1440p signals also work, but 1440p is upscaled to 4k. It works without any problems with the Xbox Series X, and because the Xbox supports both FreeSync and HDMI Forum VRR, it's confirmed that the TV supports HDMI Forum VRR as FreeSync doesn't work.