Your question is worded a little strangely and I’m not quite sure what you’re asking, so I’ll give you some general information instead of directly answering.

HDR is High Dynamic Range, so by definition you will have more colour fidelity by having it enabled (as long as your monitor also supports it).

To my knowledge, the act of grading is to modify colours to appear properly on different screens. This sometimes means reducing the gamut (for example, grading HDR footage into 8bit Rec.709), which of course means less dynamic range.