The DP signal (both video and audio parts) is generated by the GPU, and the USB-C controller just runs that signal straight through unmodified when running in DP Alt Mode. If you're running in DP Alt Mode (and since TB3/4 is a superset of USB-C, Alt Modes are Alt Modes), then you'll by definition have audio in the same way as if you used a standard DP port. No: DP puts both video and audio over the same main links. You'd be better served by connecting your LG CX to your motherboard's lone HDMI port. Unfortunately the active converter chip used does not appear to support DSC, so you're stuck with 4:2:0 subsampling for color compression, which as noted above you need to do 4K60HDR10 over HDMI 2.0b. In case you're wondering, the way that the Startech adapter you linked works is it is a USB-C-to-DisplayPort Alt Mode adapter connected to a DP-to-HDMI active converter that outputs HDMI 2.0b. 4K60HDR10 is not possible over HDMI 1.4b because HDR was a new feature for 2.0. HDR does take more bandwidth than non-HDR (10 bits per color vs 8 bits per color), and 4K60HDR10 is ~9% over the HDMI 2.0 bandwidth maximum unless you do color compression. USB3 HDMI Alt Mode is limited to HDMI 1.4b. AFAIK there's no USB4 HDMI Alt Mode yet (there's one for DP, and there's also tunneled DP over USB4/TB mode), which means USB4 falls back on USB3's HDMI Alt Mode. Something like 90% of the USB4 spec is optional (this may not be hyperbole ), so it's a total crapshoot.

USB4 is operationally TB3, which means it can operate as USB3-on-USB-C or as a Thunderbolt tunnel encapsulating various other protocols like PCIe and DP. Clarification: TB4 is just USB4 (which is USB-C only) with some of the optional parts made non-optional.

Thunderbolt 4 to hdmi cable