Macbook air m1 turning on automatically after shutdown while lid is closed

Is an external keyboard or trackpad/mouse connected where a keypress or mouse click would wake it?

Do you have it configured to wake/power on at a certain time?

Did you connect or disconnect the charger?

Even when a Mac is "sleeping", it may wake up from time to time for processing various things depending on how the laptop is configured. There is also a PowerNap feature.

Maybe the lid angle sensor is bad or damaged. You can have Apple or an Apple Authorized Service Provider examine the laptop to see if this may be the case.