Like the Hisense H6510G, the Hisense R6090G has an okay color gamut, but it’s not considered a wide color gamut for HDR content. It has good coverage of the commonly-used DCI P3 color space, but limited coverage of the wider Rec. 2020.
The EOTF follows the target curve fairly well until the roll off at its peak brightness, except some scenes are slightly over-brightened. It’s the exact same with Game Mode enabled because you can enable it in any Picture Mode, as seen in this EOTF.
If you find HDR too dim and want a brighter image, use the ‘Dark HDR’ Picture Mode with Gamma set to ‘1.8’, Color Temperature set to ‘Cool’, and Contrast and Backlight each at their max. This results in a noticeably brighter image, as seen in this EOTF. However, the image is inaccurate as increasing Contrast makes the image too blue, as seen in this color gamut photo.