We recommend creating a workflow based on Emmisive Measurement  White Illuminance.

If "Custom"  mode is selected - the user has to adjust the Monitor Brightness slider with no feedback from the instrument - which is much harder and may create a non-optimized profile.

Turn off all functions that may change monitor brightness in the future:

Automatically adjust brightness and Try Tone must be disabled!

To prevent from accidentally changing Brightness from the keyboard - disable this function too:

macOS Monterey users

Be sure to:

1. Automatically adjust brightness - turn off 
2. True Tone - turn off 
3. Select any ICC Profile but not default (screenshot: iMac). You need to profile your monitor. Before select e.g. DCID60.icc 
4. To prevent from accidentally changing Brightness from the keyboard - disable this function too:

M1 MacBook Pro with XDR Display

There are some limitations today. Apple doesn't allow any software to control XDR Display calibration. We are working on a dedicated procedure.