This is the answer that I got from the m5stack support:

The circuit design of Input power is minimum 4.5V DC. So we dont suggest with 3.7V input.

While it would not burn the board, may have some impact to the signal strength. If you are fine with the signal performance, you can use it in 3.7V

Hello,

I was wondering if there are any longtime consequences, when I power the atom light with 3,7V over the 5V Rail.

I have tested it and the controller works completely normal, but I am not sure if the step-down voltage controller can handle this over a long time.

Does anyone know the limits of the voltage controller or the exact part, that is used so I can look it up?

Thanks