ITS ALiVE!!!!!
Flashing the onboard TB3 firmware worked!
Just booted into my MacPro partition and connected my MBP to 1st TB3 port and voilá TB3 networking for the very 1st time ever in my hackinstoshes thought the years... Really, really happy
Also connected to 2nd TB3 a USB-C multiple adapter (network, USB, HDMI) and it bloody works!!!
All this without the special SSDT yet, as I have a DSDT.aml done by M@ld0n a few months back specifically for this system.
My ISP is down, no access to internet from home and typing this from my iPhone...
Will now do tests with iMac19.1 and special SSDT!