If you are so eager for the solution start reading from 2nd paragragh.
I generally cannot use PWM flickering phones. As it is mostly in the LED phones, I have avoided using LED phones and I can only buy non LED phones like LCD IPS. I came to know about PWM when I bought google pixel 3xl. It gave me daily(yes each and everyday) headaches. The headaches used to gradually increase to certain state where I am forced to leave the office work and goto home and sleep or take 2 pain killers at once and apply some balm on forehead. Saying all this to let you know my headaches and PWM relation. After learning PWM, I sold my pixel 3xl and buying only lcd phones since then.
So coming to MBA M1, I bought it last week, and for the first time usage, it gave me headaches. Generally I do not feel eye strain. I only get headaches. But that alone is nightmare in my life. I have very bad history with headaches. So, I tried to return the laptop but the Indian seller on Flipkart only gave me replacement option. I even tried to use the replaced laptop. This time I put the brightness to 100 and tried to use laptop using my sun glasses. But still I got headaches.
But, on the next day morning, I opened the laptop and disabled auto brightness and set the brightness slightly above 50%(generally you can't see percentage but I went by the placement of brightness cursor in control center). Means it should be somewhere at 60-65%. And also enabled night shift all the time. After more than 4+ hours also, I did not get headaches. Then next day I used completely with those same settings without headaches issue.
I read a review of M1 which also included M1 PWM information. Review link is provided below. In short the article is saying that, M1 has PWM at very high frequency(the higher the frequency is the lesser the issues to us generally but again for very sensitive people they get issues even at higher frequency like me) at upto 49% brightness. And also there is PWM with the same high frequency at very high brightness levels. So is why, I experimented with the above said brightness range(i.e at 60 to 65%). But even at 60-65% brightness, the screen will be very bright to look at, so for this I am using an app called Spf - Screen Polarizer. This basically provides a layer on the screen. This way the screen brightness will be shaded without actually decreasing the Mac brightness. Link is shared below.
I am not sure if this is just temporary fix or something happening in my favour because of some other unknown reasons. But just want to share my experience to fellow sensitive gadget lovers. I know how happy it feels to find a fix after suffering from long time 🙂. Also, there is another kind of solution according to one of our fellow ledstrain forum member. He shared his experience - that after increasing the work hours gradually even he is facing headaches, one fine day the headaches are gone. He is saying that may be his brain has started adjusted the Pwm after repeated forcely using the laptop.
Lemme know if this worked to any of you or not. Would be happy if at least one person find it helpful.
Also I think, this brightness range fix only works on M1 Mac. If you check your device review on notebook check.net and see if the reviewer has mentioned the PWM absent range and try to experiment your device at that brightness range.
Article link - https://www.notebookcheck.net/Apple-MacBook-Air-2020-M1-Entry-Review-Apple-M1-CPU-humbles-Intel-and-AMD.508057.0.html
App link - https://apps.apple.com/in/app/spf-screen-polarizer/id1463398888