Plz Post that youtube link !!!
Sure, here's what I've found. Actually, that one with Clover and BIOS video was not a Z170 but Z87X.
Asus Z370-A + ThunderboltEX 3:
Gigabyte GA-Z170MX:
Gigabyte Z87X (this one is actually allows BIOS/Clover):
Asus Sabertooth Z87 + ThunderboltEX 2:
Anyway, this still remains a complete mystery for me, why Apple Thunderbolt Display doesn't work with Titan Ridge onboard controller of Z390 Designare motherboard. JHL7540 in its current implementation seems to be not able to work in pure Thunderbolt switch mode which is absolutely mandatory for Apple Thunderbolt Display. Be it Windows, Ubuntu or macOS. I've tried everything and still no luck. None of the OS is able to see the monitor.
Gigabyte's engineers definitely broke something that worked fine before. BIOS and onboard TB firmware need significant work now to properly support Apple Thunderbolt monitor.
Accordingly to official Thunderbolt 3 Technical Brief:
https://thunderbolttechnology.net/sites/default/files/Thunderbolt3_TechBrief_FINAL.pdf
There are three different operating modes for Thunderbolt silicon. USB, DisplayPort and Thunderbolt. Depending on what device is being connected, the chip switches its operating mode. So JHL7540 should switch when it gets the TB device, but it doesn't.
It becomes clear for me, that for some reason Titan Ridge on Z390 Designare can operate only in USB or DisplayPort mode. And completely ignores pure Thunderbolt mode when working with Thunderbolt monitors (pure Thunderbolt, not just DisplayPort over USB-C capable).
It also completely explains the fact, that people are currently only able to connect USB devices (various drives and TB storage solutions, external audio interfaces) as well as displays that require only DisplayPort portion (they are typically offering fallback via DP over USB-C instead of being a pure Thunderbolt capable).
In conversation with Intel engineers I've been told that there is also a power delivery controller which is a specific companion to TB chip. It helps to properly select and switch mode and adjust the power settings so the device can connect. And it is all currently up to motherboard vendors how to properly implement these things both in hardware (actual PCB layout) and software (BIOS and firmwares).
My guess is this issue may be due to faulty or very early BIOS or Thunderbolt or Power Delivery controller firmware code for this motherboard model. I already sent an eSupport ticket to Gigabyte where I described this problem. Hopefully, they'll fix something in the next BIOS updates.
On our side of things, there's also a lot to be done to get a proper Thunderbolt support in macOS. Accordingly to
@kgp researches it is still not possible to achieve a complete, fully initialized Thunderbolt Local Node implementation on Hackintosh. When it's done right, it is a completely expanded and filled with devices (all switches and TB ports with properly initialized and assigned DPIn and PCIDown Adapters) sub-tree inside NHIType3 Controller device in IOReg.
Unfortunately, in our Hackintoshes, we're only getting empty IOThunderboltLocalNode and IOThunderboltPort in the end of that tree. Of course, we have implemented DSB1 and DSB4 as well as DSB2 with mapped Titan Ridge XHC controller ports, but that's still not enough.
I do believe that with proper and complete Thunderbolt SSDT patch or even better – with a proper Thunderbolt kext (just like we use for Ethernet or Bluetooth or USB or anything else) or even with a EFI driver, it will be possible to fully initialize the Titan Ridge on Hackintosh.
Now we're only half way there. But we'll make it happen one day!