Thunderbolt Controller missing after BIOS update issues

[didlix]

I recently bought an Asus Rog Strix Z790-I and 14700K with the intention of using it with my productivity monitor that only has a thunderbolt input.

 

This was working okay, however sometimes the machine would just not boot unless I plugged in another display via USB-C -> DVI adapter, and then booted immediately.

 

I decided a BIOS update was in order. My MB had 1303 installed, and 1801 was the latest. This update did not go well and I ended up with my CPU Q-LED on, and the fans spinning up and slowing down repeatedly. 

 

I managed to install 1303 again but could now only connect a display using the hdmi out on my board or discreet gpu. I checked all motherboard settings ensuring that everything was correct.

 

After much troubleshooting I noticed that windows does not list a thunderbolt controller, nor any devices with exclamation marks.

 

I went through every bios revision, and cmos resets, and setting and still no joy.

 

While I wait for ASUS to get back to me are there any other diagnostic steps I can take? I have a EFI shell but don't know how to use it and am about to boot into linux to see if it's aware of the thunderbolt controller.

 

TIA.