Based on your question I went back through this thread to reread posts about the GC-Alpine Ridge.
I may have made a mistake in recommending this card for the Designare Z390! Those who posted
in this thread are actually using a different motherboard with a THB_C header.
There is, however, a report of someone using GC-Titan Ridge on this motherboard to drive a 5K monitor properly. But I looked at their IORegistry output, which shows that RP05 (on-board Titan Rigde) was disabled.
My suggestion at this point:
- Let the GC-Alpine Ridge card arrive and give it a try.
- It can be replaced with the GC-Titan Ridge if necessary.
But there are other options:
- When the LG monitor arrives, connect it directly into one of the on-board Thunderbolt 3 ports and take a look at the quality of the displayed video.
- Is the video quality acceptable?
- Also connect the LG monitor to the AMD GPU via a DisplayPort 1.4 cable.
- Is the video running at full 5K and is it acceptable?