Add key to driver?

using 2.93

I’m not super familiar with drivers. I have a latch that closes a lid, similar to one that you’d use on a pelican case. So the latch swings on an arm. I figured, why not just create one driver for the latch open/close sequence that I can animate?
But I can’t figure out how to add a keyframe. I can edit the two that it creates, change the key frame, the interpolation type, move the handles, etc. But I’m going to need to add a keyframe in the middle of that. I just can’t figure out how.
For this, I need the animation to be shaped more like an M rather than a /. You can’t make an M with 2 points and a couple handles.