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This is very interesting. Notebookcheck seems to have tested this device. Is this the correct model? https://www.notebookcheck.net/Apple-MacBook-Pro-16-2023-Review-M2-Max-challenges-GeForce-RTX-3080-Ti.694175.0.html
They found PWM even at 100% SDR brightness. However, what they didn't test was HDR or to manually increase the brightness further. If you had a sensor you may want to test if the flicker gets reduced at those higher brightness levels. The PWM frequency is rather low with 14 kHz, and has large amplitudes, so a cheap sensor setup would probably do. You can find devices and ideas how to measure flicker here: https://ledstrain.org/d/312-homemade-oscilloscope-to-detect-pwm-diy-guide (throughout the comments).
Temporal dithering is harder to measure. Notebookcheck tried to do that here: https://www.youtube.com/watch?v=kFS7WWxKyuY