What is the shortcut for changing my primary display? What is the shortcut for switching the primary display when two monitors are connected. It is cumbersome to open up System Preferences > Displays and drag the menu bar across each time I switch.

Background: I have a makeshift IKEA standing desk and two monitors. One monitor is on my standing desk and the other is directly on the table (at sitting level.) Because I switch between sit/stand positions often, I want to switch the primary display so that all of my open windows are on the monitor I'm working on.
It's not 100% clear how you're using your screens, but perhaps the following will work for you.

Let's assume your Primary monitor is on the sitting desk. When sitting this is fine, but when you're standing you could just use the Command + Brightness Down Keyboard shortcut to turn display mirroring on so that what's on the sitting screen appears on the standing screen. Then, you can use the same keyboard shortcut to turn display mirroring off when sitting again.