I'm pretty late to the party, but for people who later stumble upon this post like I did:
It is both PCIe 3.0 x4 AND PCIe 4.0 x1, as was already the case with the V2 that I have.
The Acquantia AQC113CS chip switches to PCIe 4.0 x1 when it detects PCIe 4.0 capability.
The way I found out was a...