> The problem is that you can’t use the 16” with an external display and the lid open without the fans spinning at full speed.

I had the same problem, when connected to a USB-C monitor I wanted to use the keyboard, but not the built in monitor. Even with the display backlight off the fan would still run. After a lot of searching I found that you can disable the built in monitor by:

- Booting into recovery mode - Opening Terminal - Entering `sudo nvram boot-args="niog=1"` - Restarting - Close the clamshell - Plug in the external monitor - Open the monitor

I hope that helps.