Haven't used this app for ages, but yesterday I fine-tuned the HDR settings for my newly bought laptop under KDE/plasma, definitely on Linux. That readme might be outdated (or the tool doesn't work on KDE at all)
Yeah I think I’m a bit outdated here. But I do think Linux hdr support is weak enough that many Linux-oriented apps are unlikely to do it well
My understanding of the landscape currently is that KDE Plasma is the only major DE that supports HDR. I use it for Steam for that reason.