I'm interested in using my LG UltraFine 5K with a Windows computer. Preferably I'd like to utilize the full 5k rendering resolution. I've seen some videos from 2017 and what they state is that back then driving a 5k display over a single cable wasn't usual at the time, requiring at least 2 displayport cables
The way Apple managed to make the MacBooks drive the LG 5k through a single cable is by combining two Displayport 1.2 connections to the TB3 port. Thus any non-Apple systems wouldn't be able to drive 5K over the single cable but would be capped at 4K.
Two DisplayPort connections over Thunderbolt is not specific to Apple. PC's can do it to as long as they have a Thunderbolt 3 controller with two DisplayPort 1.2 or better connections to it (internal or external). Some motherboards might have only one DisplayPort connection to their Thunderbolt 3 controller. If you get a PC with Thunderbolt 4, then they are guaranteed to have two DisplayPort connections to a Thunderbolt port. If you get a PC that supports a Thunderbolt 3/4 add-in card, then you can get an add-in card that has two DisplayPort inputs and connect them to any GPU (but it should be the same GPU for dual tile displays such as the LG UltraFine 5K).
I'm wondering if it would be possible to hook up the LG UltraFine to a Windows machine over USB C supporting DP 1.3+ and have access to 5K rendering resolution out of the box with a single cable.
The LG UltraFine 5K only supports HBR2 link rate. The best you can get with a single HBR2 DisplayPort connection to the LG UltraFine 5K is 5K 39Hz even though HBR2 should have enough bandwidth for 47Hz 8bpc or 60Hz 6bpc.
The Apple Pro Display XDR is also limited to HBR2 link rate (except for a special Thunderbolt mode that supports two HBR3 connections to allow 6K60 10bpc on Macs that don't support DSC). It can do 5K60 6bpc with a single DisplayPort connection.
The Apple Studio Display is also limited to HBR2 link rate. It can probably do 5K60 6bpc with a single DisplayPort connection but I don't think I've seen anyone try that.
Macs don't have a method to select 6bpc except I created a Lilu/WhateverGreen patch to do that with old GPUs such as the Nvidia Kepler GPUs - but I probably need a pixel clock patch to get 5K60 6bpc.
TB4 should at least theoretically be able to achieve the bandwidth as a minimum requirement.
TB4 has the same bandwidth of TB3. TB4 is guaranteed to support two DisplayPort connections but TB3 is not. All TB3 Macs support two DisplayPort connections per Thunderbolt bus. PCs don't guarantee anything for Thunderbolt 3.