Here’s a fun one. On some Macs the screen brightness keys are actually recognized as the F14 and F15 function keys. Which means when you build your own keyboard with those keys they change the screen brightness. Yuk. I found a post that explained how to change that, which involved going into System Preferences -> Keyboard -> Shortcuts -> Display, except… it’s not there. (See the image above? Not there.)
But wait, it is there after you plug in a device you built that has F14 and F15 keys. (See below.) So once you plug in a device you built that has F14 and F15 keys, the Display option will appear and you can disable the brightness thing by deselecting things. And yes, you can still totally adjust the screen brightness by using the keys on your normal keyboard.
This post is about 95% for future me, and 5% for someone who needs to figure it out and finds this post. You’re Welcome!