Have to comment that this is just completely wrong and we need to stop telling ourselves this. I’ve experienced a lot of pain with EMs who have no idea what is really going on in a codebase because they have little domain expertise, no idea what tradeoffs are made by developers, and, crucially, do not ever punch the keys and commit anything. Why? Because frankly, they already have the job.
If you don’t ever interface with the codebase and don’t really understand what it does, but you still feel so inclined to steer the ship, you’re a product manager, not an EM. Possibly worse because there is more credence given to you? This is most likely advice for someone who just wants to issue vague edicts to a team that frankly does not need them.