Almost everyone here get the technical details perfectly. That is not the issue here since anyone with a viable brain is able to read a web page that explicitly states that the 1000 nits are reserved for HDR use and that in SDR there is a maximum of 500 nits.
What many criticize here, and rightly so, is Apple's way of mentioning figures that necessarily need to be checked in a side page to see which conditions apply. Especially when this way of indicating luminances during keynotes does not correspond to the way of stating it for other products of the same brand.
There was the same problem with for example the "x5 zoom" of the iPhone 12 PM which is indeed true if you go from ultra wide angle to telephoto. But we're really dealing with commercial terms that are factually correct but deliberately obscure that will mechanically trap consumers who are less enthusiast than people who go to sites like MR.
Don't get me wrong 1k nits in SDR display is very uncommon once again that's not the issue. The issue is Apple's way of statings luminances which is shady since most users are watching SDR content most of the time and most users will don't double check luminance conditions if they are not clearly stated on keynote / main page.
Sure, but the display hardware is capable of going to 1000 nits and I want to use it. I'm bummed that they're limiting software to prevent it from taking advantage of this. It's like a car company preventing the gas pedal from working if you're going over the speed limit.
I bought my 16" with the knowledge that it would likely be limited to 500 nits for SDR. However, I'm disappointed that there's nothing in the display settings to allow me to go further. In theory, I should be able to "calibrate" the display to go brighter.