Yep, the problem with the compatibility layer is that a game can be very particular about the version too.
You're very welcome. This is after all, the essence of Arch. Now you know what is happening and why HDR is not yet widespread on other linux. On the other hand, you get to experience HDR gaming when other distros may not yet support it.
I can confirm that I do have the same issue regarding brightness. However, I never tried to investigate further as my mechanical keyboard has a fn keys to adjust brightness (fn + f1/f2) so I don't need to open settings to wiggle the slider. I can understand that it can be an issue for others. I suggest reading more regarding display and monitor. If all else fails, try asking the forum. I think it is DE specific (because wayland).