So I have been trying to get my Raspberry Pi 3 B+ to work for a couple days now. Here are the issues I am encountering:

On stock Kali image, airmon says it's missing nexutil. I noticed in the arm images, there is RPi2/3 and then RPi2/3 without nexmon but I am using the one that doesn't say without nexmon.....
On Re4son's kernel, after a while of scanning (like 4-5 min) airodump says that it's on fixed channel: -1 and it is no longer capturing packets...

Why do you need to do mon0up/down now? Why does Airmon-ng not put the adapter into the proper mode?

Side note: How hard is it to toggle the GPIO in kali?