If I buy that SilverStone CP14, that allows me to convert from the 19-pin header to the new 20-pin Key A standard which supports (from my research) a single USB-C output or two USB-A outputs, is that correct? But is that CP14 converter limited to 5 Gbps speeds regardless, because the 19-pin connector is only meant to support 3.0/3.1 Gen 1? Or does it magically pair together the two 5 Gbps lines intended for separate USB-A connectors into a single 10 Gbps (3.2 Gen 2) USB-C output?

How is that different from this?

My new PC build is a small form factor case with a Mini-ITX motherboard. So there is only one PCIe slot and no space on the back for a PCIe card besides the GPU. (There happens to be a small plate above the GPU which I plan to replace with a 3D printed part with USB-C output(s) though). So (besides maybe my extra M.2 slot) there is only the 19-pin header that I can use to provide me with USB connectivity (aside from the slow USB 2.0 header, which I'm happy to ignore entirely). So I won't be able to use your suggestion for the second two links in your comment.

But my question, now, is whether I should buy that CP14 converter or another single-USB-C-port converter like FIGURE 2 or just build my own two-USB-C-port adapter from FIGURE A + 2x FIGURE C. The CP14 converter might give me 10 Gbps, FIGURE B will give 5 Gbps, and the combination will give two 5 Gbps ports. Is there anything else I am missing before I decide whether it's worth having two 5 Gbps ports instead of one 10 Gbps port?

Also, I cannot actually find anywhere to buy the CP14 product, it looks like it is not out yet. But does this product work just as well?