I had an issue this morning that may apply to the Z390 Designare build. (I'm using a similar mobo, the GB Z390 Aorus Xtreme Waterforce.) The TB chip was flashed with the modified Aorus Xtreme firmware. MSR is unlocked; NVRAM is working. Bootloader is OC.
I had no issues using a TB drive when testing this new build. Now that the rig seems stable, I connected it to a CalDigit TB dock and started noticing panic re-boots on shutdown (happened with both Mojave 10.14.6 and Catalina 10.15.4). Initially, I thought it was due to the latest changes in OC V057, but it was problem with a BIOS setting.
The panic re-boots only occurred when the dock was connected; when disconnected, there was no panic re-boot on shutdown.
On a BIOS re-set, I'd left "Wake From Tunderbolt(TM) Devices" enabled. If this is enabled and the dock is connected, there are panic re-boots. Once this setting was disabled, the panic re-boots stopped and the dock could be left connected.
Again, I don't know if this applies to the Z390 Designare, but if it does, hopefully the info will save time for someone else.