My monitor needs to be at maximum brightness to disable PWM.
Most monitors have a custom RGB preset where you can adjust the R, G, B values individually.
This is done for colour calibration purposes, however it can also be used to dim the display while leaving the backlight at maximum.
You could for example set RGB all to 50 (0-100) or 128 (0-255) on all of R, G, B or whatever number is appropriate for you and your lighting conditions.
Then you can just flip between Standard and your custom preset as desired.