During the final, twelfth stage in the Stray titled the Control Room, you have to solve a puzzle to disable the system lock. From our walkthrough, you will learn the required steps - we've described how to successfully hack the terminals.
Puzzle location - Control Room
In stage 12, the game's final stage, you first have to get to the main control room.
This is accomplished by starting the machine, pulling it up, and leaping on it while in synch with B-12.
In the control room, you have to examine the main computer and run over the keyboards of the nearby stations to activate them.
This way, you'll learn that the system is locked and that you will have to unlock it by hacking.
Hacking the 3 terminals
There are 3 terminals in the room which you can activate in any order. You will recognize them by the padlocks displayed on their screens.
You need to find a panel near each terminal. Interact with it and then scratch it to damage the cables.
Doing this will allow B-12 to hack in, but first you need to give it the correct command while facing the blue screen.
Connecting B-12 to the system
After hacking in 3 times, B-12 will stop working. Pick up B-12 and move it to the location where you previously learned about the system lock. By placing the drone in the rectangular field, you will proceed to the ending.