Even though the manager is an authority figure, the best engineering managers acquire power to give it away.
What this means is they will establish ownership over a space and then give control of it to an engineer on their team to help them grow. This is especially important growing engineers to senior levels and beyond.
By making the engineers on the team share authority, the team becomes more resilient, so that it doesn't collapse when the manager is out.
Alex's Instagram example:
The oncall in his org was very weak and unhealthy.
His manager got the ball rolling and collected a working group of senior+ engineers and managers to align on the problem and agree to solving it.
After his manager established a sphere of influence here, they handed it over to Alex to lead the entire effort and successfully revamp the oncall system for ~25 mobile engineers.
Manager easily could have led this effort themselves but chose to delegate to Alex, so that he could build authority in this area.