How to listen very, very well such that you understand the speaker's point of view, and they feel heard and valued.
How to tell someone that you - as the appointed decision maker for a specific thing - heard and understood their point of view, and nonetheless that your decision is in favor of a competing point of view, without making it personal and without demotivating them to form their next point of view.
How to signal fuck off, you're wrong with regards to this one specific, situational issue without harming the relationship.
How to say hey can we talk about this first, and I'd like you to listen and consider my side before you make your final decision without signaling that you're whining or insubordinate.
How to cultivate interest in other people's lives, get to know people on a personal level and even "make friends at work", without letting yourself fall into the trap of cronyism / nepotism / etc when it comes to job-related situations.
How to hold back on expressing points of view that are not wanted, needed, fully fleshed out or invalidated by evidence that you're for whatever reason discounting or ignoring.
How to be consistent in your decision making and communications, even when you don't feel like it, are sick, are stressed, are depressed, it's raining and grey outside, a big weekend trip is on the way and you're checked out.
How to signal that you're angry or frustrated or that the current plan is a bad one without having to say it out loud.
There are others, these are just a few that came to mind after a friend asked me "So I think I know all the tech stuff, and the people stuff, and the process stuff, what else do I need to know about becoming an EM?"
In my opinion, if you're very good at this kind of stuff, you can be a baseline C- performer as a leader, even if you're lousy at the other aspects of management and you don't know the field you're in at all.
Also in my opinion, if you're not good at this kind of stuff at all, no amount of skill or talent at the other aspects of management will elevate you past a D+ as a leader. Maybe you could get an A for a little while. Six months or a year. Over time though, your people will despise and undermine you, and your peer managers will undercut and overwhelm you.