One thing that wasn't mentioned is the max sustained screen brightness for SDR, which is higher on the M4 Pro (1000 nits) compared to the M4 Air or M1 Pro (500 nits).
There’s an awesome app called Vivid which just opens the HDR max brightness. I use it all the time with my M3 Pro when working outside and I believe it also works on earlier models.
I would personally be afraid of using that in case it causes damage long-term to the screen either due to temperature or power draw or something. Idk if there are significant hardware differences but in this case I would guess there’s a real hardware reason for it?