What I found interesting that Apple used internal floating-point representation with some values ABOVE 1.0f but those values probably can't leak into final video, at best they might remain inside OpenEXR image format captured at some point "as is" (?)
Reference Mode
Reference
mode is a new display mode for color-intensive workflows that pin
settings and block out distractions to provide more objective and
reliable reference results for a variety of common videos, such as color
grading, editing, and content mode, similar to the reference presets on
macOS.
When you enable the reference mode, you will have the following features:
- The SDK peak brightness is fixed at 100 nits and the HDR peak brightness is fixed at 1000 nits, so there is a 10x EDR headroom.
- Disables HDR tone mapping to provide one-to-one media display mapping.
- Disables
all display dynamic adjustments that occur to adapt to the environment,
such as True Tone, Auto Brightness, and Night Shift modes, and instead
allows the user to fine-calibrate the white point manually.
=== end of quotation ====
At least back in 2021 Apple was still using Metal (their Vulkan-like graphics API) and OpenGL for system-wide compositing, not sure if it changed or not lately?
Still I am not sure how this provides HDR-like experience on SDR display (may be by using dynamic mapping?)
Of course this is just tip of the iceberg I found in few minutes at the morning.