Also with the M1 Pro MacBook, my LG USB-C monitor broke during the upgrade. Black screen, same on another connected USB-C laptop. Tried different cables, unplugging power from the monitor and factory reset on the monitor, no luck. Other inputs like HDMI and DisplayPort still work. I don't think the breakage during the upgrade is a coincidence.
I would really advise against having anything connected to the Macbook during upgrades, except the charger...
I would really advise against having anything connected to the Macbook during upgrades, except the charger...