This is most likely not due to the cable. Even Cat 5 cables can be used for 10Gbps data traffic over short distances, although you could of course try out whether changing the cable would increase the speed.
However, 10Gbps cards usually get quite hot, which can lead to a reduction in speed. Possibly placing a fan next to it could help.
Are there enough PCIe lanes available? The card requires at least x4 PCIe lanes for 10Gbps transfer.
Otherwise this could also be a driver problem. It certainly wouldn't hurt to contact TP-Link directly.

If it helps, I also had a maximum of 2.5 - 2-6 GB download on Windows 10, and after installing Windows 11, I get 4.3 GB, without having made any hardware or software changes, the rj45 is a cat.6a.

I have 8.5 GB with cat8 cable and iWay.ch provider