Isn't like ... 200 nits ... a healthy upper limit for looking at a screen all day?
If you are a dark area 200 nits would even be high.
If you are in a well-lit area or outside in a sunny day, 200 nits would be super dark, and by that definition if it was unhealthy, looking at almost anything in a well lit day would be unhealthy.
Thus, I'm assuming indoors.
The current MacBook keyboards are quite nice, they have the same mechanism as the external Magic Keyboard sold by Apple, and they seem quite resilient. I had no stuck key in the last 2 years.
The prior model of Magic Keyboards with the Fn key use older defective dust-vulnerable switches.
Note that I bought the 2018 or 2019 model with extra isolation under the keys. That didn't help at all.
The keyboard worked perfectly fine.
I haven’t had a chance to test the 2019 Intel MacBook too much, but the M1 2020 was heavily used outdoors. I believe the M1 2020 model was the first one to get the Magic Keyboard mechanism: https://support.apple.com/kb/SP824