The upgrade to macOS Big Sur seems to be causing problems booting on their MacBooks for some users. There are indications that the upgrade is causing problems with the laptops I / O boards.
According to a user’s inventory, these are at least dozens of reports about laptops stuck on a black screen while the upgrade is in progress. The keyboard has stopped working and Apple seems to recommend that users send their laptops in for repair. In most cases, these are MacBook Pro models from 2013 and 2014.
A Reddit user disconnected the I / O board and then the upgrade went through. After replacing the board with chips for wifi and bluetooth, the laptop works properly. Another user unplugged the board for the upgrade and that seems to work too.
It is unknown exactly how widespread the problem is. Apple released Big Sur last Thursday and has not yet responded to users’ concerns.