"I have spoken" is how Kuiil, one of my favorite characters in Mandalorian, communicates that his decision is final. It's usually deloyed just before Mandalorian plans to offer a rebutal. It helps that Kuiil is often in the position of power. If Mandalorian wants his help, this is the way it's going to be.
Another example of "We're done debating, this is my position" comes from the movie the Irishman when Frank is told to tell Hoffa, "It's what it is." It's also used to clearly communicate this is the final solution. And again, it comes from a position of power.
We should listen to other perspectives. We should consider other points of view. But in situations, were we are the decider, and we've made up our mind, have a clear and firm way to communicate "this is final and now closed for debate" that is more effect than the over used, "because I'm your mother/father/boss, that's why."
I also find it more empowering than "I guess we'll just have to agree to disagree." That phrase has often rubbed me the wrong way, because we don't agree to disagree, we acknowledge that we disagree. Disagreement is good and expected. Don't shy from it.
By the way, I test drove "I have spoken" in a meeting at work the other day. The context was different. I wasn't the decider. I was simply providing some feedback. The person I was sharing it with was telling me basically, thanks for sharing, but we're going to do it my way. So I concluded with "I have spoken," simply meaning, I've shared my feedback, you can do what you want. Luckily, the person knew the reference and laughed and got the point.