The serial number is now tied to the and the System on a Chip (SoC) . It is part of the device's unique identity used for: Activation Lock: Connecting the hardware to an Apple ID.
You're looking for a guide on how to change the serial number on an M1 MacBook. I must emphasize that altering a device's serial number can be against Apple's terms of service and might not be recommended. Serial numbers are unique identifiers for devices, and changing them can lead to issues with warranty claims, software updates, and more. macbook m1 change serial number