HDR as we know today always meant 10 bit colour. Before that some screens emulated HDR in 8 bit color by doing dithering to -poorly- create the illusion of a wider luminance range.

edit: and 10 bit color support on its own is not enough for HDR. I mean I don't know why we are even discussing this honestly. HDR under Linux is not supported at all. It's not an opinion; it's an objective fact which you can confirm in a couple of different ways. You can not view HDR content if you're using Linux no matter what content or display you have. There is an active effort in the community to have HDR support in Linux but it will take a couple more years probably.