16 Pro - iMac Pro - Multi Issues

Hi all.

I run Zorin on my Toshiba laptop with zero issues, thought Id try it dual boot on my iMac Pro (2017)...mistake so far.

I'm just going to list the things that I've run across and have tried a few things found in this forum but to no avail. Please assume I haven't tried anything or have done it wrong. Not that familiar with Linux but I'm ok with Terminal.

External Apple Cinema Display - Works for about 20 seconds then starts flashing. Unplug it, plug it back in, repeats.

Sound - Only shows dummy output device even after trying a few things I've seen on here...until i plug in the second display it it plays through that just fine. But with the flashing screen issue that's not usable.

Dual Boot - After install following very specific dual boot instructions, I cannot get into the boot menu no matter what key combination I try on a pc keyboard (tried all 4 USB ports). My Apple keyboard is seen on the bluetooth list as not set up but is grayed out. It doesn't work as a boot menu keyboard anymore.

Any and all support would be greatly appreciated!

Here are some screenshots.

Screenshot from 2024-07-02 15-40-44
Screenshot from 2024-07-02 15-41-21
Screenshot from 2024-07-02 15-42-07