@CaseySJ Huge congratulations on the successful build! Thanks for the hard work on this.
I came up with a very similar config, but with i9-9900K CPU so I've been watching your progress here with a great attention, while waiting for all of my ordered hardware to arrive. So now, everything is working great in my build, except one, very important thing for me: Apple Thunderbolt Display doesn't work. I'm really in love with this display, but still can't manage it to work in my new system.
I'm using DP/DP cable from DP output of my Sapphire RX 580 to DP input of the Z390 Designare. And then I connect my Thunderbolt Display through the Apple TB3/TB2 adapter to one of the two Thunderbolt ports of the motherboard.
Have been playing with various BIOS settings, connecting and reconnecting monitor before boot and after macOS load. No luck.
Before building this machine, I've been using my old MacBook Pro 2012 with Apple Thunderbolt Display.
Maybe there's a benefit of having a working mbp+tb display combo, so there's a chance for some kind of dsdt patch/acpi fixes/any other info extraction.
Really hope to make Thunderbolt display to work with my new system. Highly appreciate if someone can point me to the right direction to solve this.