The real problem is that 400-600 nits is allowed to be called a “HDR-certified” display. For “real” HDR you want at least 800 nits, ideally 1000. Otherwise you

The real problem is that 400-600 nits is allowed to be called a “HDR-certified” display. For “real” HDR you want at least 800 nits, ideally 1000. Otherwise you have to do what is stated upthread, latch max brightness to whatever your maximum nits is and make everything else very dark to keep the relative contrast intact.