If you are not outside in bright sunlight it’s almost certain that your screen is not at its highest brightness in the first place.
All HDR is doing is adding more range between the darkest element and the brightest element.
I.e., if you go to this webpage and set your screen brightness to maximum, the HDR effect visibly goes away because you’re already telling your screen to maximize brightness everywhere. Put the screen brightness at 50% and the HDR effect is visible: the bright parts are brighter.
What are you talking about? I have a HDR display, in Chrome on Arch the literal only change in the submission's demo is the brightness of that particular element, doesn't change anything else on the screen, sounds like you have a broken HDR implementation.