[abhibeckert]

Both QR codes are using #ffffff.

The "bright" one has metadata that tells the operating system to render white at the maximum possible brightness, instead of whatever brightness it would normally render white at.

It's broadly supported on Apple devices, though how well it works depends on the hardware you have.

[tuukkah]

You're correct in part, as both image sources (the picture and the video) have maxed out pixel data. If it's HDR10, it does not have 24 but 30 bits of color though, so it maxes out at #3fffffff.