The SSDs of 2015-2017 macbooks start failing and they are soldered on the board. I have a 12" that I can only boot from external now otherwise the device would be dead. With the M1 models you don't even have the chance to do this. Apple won't even change the failed ssds they will sell you a new logic board for the prize of a new machine. It's infuriating and the only reason I won't buy a machine until they make user replaceable storage the norm again.