I am investigating whether a macOS display utility can adjust the luminance of normal SDR desktop content system-wide, including other apps, on the built-in Liquid Retina XDR display of a 2021 M1 Max MacBook Pro. Is there a documented public API, or combination of public APIs, for this scope? The research target is SDR white around 1000 cd/m² while retaining HDR highlight capability, where supported by the hardware and OS. This is a feasibility question, not a claim that this output has been achieved or is supported. The approach must preserve OS color management and respect thermal, power and brightness limits, including protective dimming. I am not seeking gamma-table changes, screen capture and HDR re-display, private APIs, or bypasses of system protections. I understand that enabling EDR for an app's own layer is different from controlling ordinary SDR content in other apps. I am specifically asking about the latter. If this is supported, could you point to the API names, primary documentation, applicable macOS versions and hardware limitations? If it is not supported through public APIs, an explicit clarification would also be helpful.