I have never used an HDR display before so I'm not sure how it's supposed to look.
I have been playing Spider-man both with and without HDR and unless I'm staring right into the sun there is literally no difference. I have always heard people talk about HDR as something incredible but I'm honestly disappointed.
I also played Tetris effect: connected and HDR seemed to just make all the menus darker, but the rest looked the same.
Have I done something wrong or is this how it is supposed to be?
Aren't there different "levels" of HDR? Most cheap TV's only support HDR10 which basically does nothing. I wouldn't be surprised if that's the only quality the Steamdeck supports too. I haven't checked the specs though.
That's not what HDR10 means at all, it's just a different data encoding standard. Like Blu rays vs HDDVDs. A properly encoded HDR10 looks just as bright/dark in a proper monitor