Using @CaseySJ's opencore configs from
HackinDROM app I have thunderbolt ports working with hot plug and also am able to drive a monitor from the IGPU via a displayport connection on my TB3 drive enclosure. To be honest with you, I plugged in the enclosure booted from Catalina and it found the enclosure. I plugged in the enclosure in windows and it went blue screen.
hah!
Using the displayport via the TB3 enclosure the LG ultrawide monitor I'm using will work at 3440x1440 @ 120hz with HDR using only IGPU. If I plug the monitor in the HDMI from the back of the motherboard the monitor only gets 3440x1440 @ 50hz (no HDR).
This only thing that I'm most positive I don't have working is sleep, which I never use. It takes about 20 seconds to boot the machine so if I'm not using it for an extended period I just shutdown.