This cable mates to the connector on the mainboard: https://www.digikey.com/en/products/detail/i-pex/81466-100B-02-D/14312108
It has an identical IPEX Cabline-UM connector on both ends (with flipped pinouts!), so you’ll need the board mounted receptacle and a custom PCBA to do anything useful with it. https://www.digikey.com/en/products/detail/i-pex/20879-040E-01/14312094
This is the only mating cable I’ve been able to find that is available in single quantity. Soldering the receptacle by hand can be challenging, but is very doable. I used a paste stencil and a hotplate to reflow it.