FP4 - Stuck in fastboot mode - relock the bootloader

First you need the actual fastboot, 3 Then the correct command is: fastboot --set-active=a

Fastboot commands ; set_active slot> Sets the given AB booting slot as active On the next boot attempt, the system boots from the specified slot For AB

fastboot change slot Super Partition Dynamic Partition A & AB Slots Fastboot Detailed Guide munchy•55K

fastboot getvar currentslot fastboot getvar current-slot current-slot: b Finished Total time: fastboot --set-active=b Setting current slot to 'b' OKAY