In the last few hours, in addition to iOS and iPadOS 13.4 and macOS 10.15.4, Apple has also released the version 2.2.2 of the firmware for the Pro Display XDR , which adds support to the reference mode custom.
In a new support document, Apple says that users can create reference modes suitable for various environments and workflows of production by choosing different options regarding the color gamut, white point, luminance, and transfer function SDR.
To check the firmware version of the display you need to click the Apple logo> about this Mac> Report system> Graphics / Display.
After upgrading to the Pro Display, the XDR may be prompted to restart. Otherwise, the update will be installed the next time you disconnect and re-conversion of the display to a Mac or to the power supply.