What's fun and shows that color images will indeed be overexposed is if you right click and inspect element on the whiter text and change it to an emoji or something, the result is super overexposed. You can change the <p id="tester"> to <div id="tester"> and then toss an <img src="URL here"> in the div with the image URL of your choice and it'll attempt to display the image at the crazy high brightness. All are overexposed.
I still think it should be plausible to add a "daylight mode" at 600-700 nits to help with outdoor visibility just like there's night shift for nighttime viewing. The display is clearly capable, it would just need to be set up correctly to map white to a brighter value.
That's because the page doesn't exploit HDR. It exploits EDR, Extended Dynamic Range, which works simply by pushing Gamma values linearly to absolute max and does indeed cause clipping. It does not care or worry about anything other than absolute white gamma. This is also why it's misleading to use this same source code to display anything other than white and say that those other things are clipping because of poor color profile mapping. That is not true. Safari is content-aware and can map sRGB vs DCI-P3 properly for instance.
Pushing gamma is the trick Apple has employed for years to make Mac displays brighter. It is not without flaws, though. See here:
It's not very interesting to end user ultimately, though. What end user needs to know is:
1. Apple has full control over the display and EDR used to make sense for displays that could not physically display brighter brightness. But it does not make sense for the new MacBook, which can physically display brighter brightness values than whatever the max SDR value is.
2. Currently the 500 nits limit in SDR is artificial rather than absolute. The hardware device (the display) is absolutely capable of even brighter values.
3. Sure, some professionals want to mention their working environments and low nits. I do concede this is valid but... again,
these nits values are dependent on the viewing environment. It is extremely misleading to say that these are absolute values.
Anyone claiming to be "professionals" viewing displays at 80-120 nits all the time in any viewing environment do NOT understand what they are talking about AT ALL. I don't care how many years of expertise you have in the industry. The FACT is that there are technical limitations only engineers can understand and colorists ARE NOT engineers.
So it is plausible to use >500 nits of brightness for any of the new MacBooks by "hacking" the system into thinking everything is HDR. The reason it hasn't been done already is because many developers think Apple can very easily flip this switch in the next update, and
it is absolutely pointless to try and hack the system when Apple can change it at any random time. It doesn't have anything to do with the difficulty of achieving the task.