I've had the M1 Macbook Air for two days now. I'm coming from using a 2017 Macbook Pro 13 which was working very well for me. I'm still uncertain how this new macbook is for my eyes overall, but the settings I think work best for me are True Tone Off & using the Calibrator Assisstant to set the white point to the lowest. This is the same as I had on my 2017 Macbook, which didn't have True Tone. I can't be 100% sure, but I think True Tone actually makes my eye strain noticably worse.
Also, for me personally, Night Shift seems to cause more discomfort if set too high. During the day, I barely use it or set it to 1/4 or 1/8 on the bar. At night it's set to auto on the halfway setting, but I sometimes lower it if I feel it's causing strain. I've also downloaded QuickShade for when using the Macbook in a dim room. It creates a screen overlay to artificially lower the brightness past the display minimum.