I agree with what you said, but I was trying to give the layman summary ;)
> The SDR content is dimmed proportional to the increase such that SDR has the same emitted brightness before & after the change.
That's the intent, but because things aren't perfect it actually tends to get darker instead of stay perceptually the same. It depends on which panel you're using. MBPs are prone to this, XDR displays aren't.
> I agree with what you said, but I was trying to give the layman summary ;)
Your layman summary is wrong, though. Brightness stays the same is the summary, whereas you said it gets darker.
> MBPs are prone to this, XDR displays aren't.
On my M1 16" MBP it doesn't have any issue. The transition is slow, but the end result is reasonably aligned to before the transition. But yes MBP displays are not Apple's best. Sadly that remains something exclusive to the iPad