[liminalsunset]

The iPad Pro 2020 uses a PWM frequency of 60kHz or so, and only under 13% brightness according to NotebookCheck. This is unlikely to be a problem.

True tone, iirc, is a simple color temperature adjustment of the screen. I wonder what happens if you enable Night Shift manually and set it to how it looks with true tone on, and see if it triggers the same problem. You can try the same experiment with your computer. Perhaps it is that color scheme that is causing you the issues.

Apple iDevices have a feature called Color Filters in Accessibility settings, which allows you to manually change the color tint of the screen. It may be of interest to you to see if a light tint helps the screen be more suitable for you.