The QNAP TVX-h874T has two PCIe slots. One comes loaded with the Thunderbolt interface. One is empty. The base box has two 2.5 GbE ports. If you want higher speeds, you need to install a PCIe card. I ordered one with two 10/25 GbE ports.
QNAP’s instructions say to do the following.
But I couldn’t get at the screw in question. The power supply was in the way.
I ended up detaching the power supply and swinging it to one side:
Then I was able to install the card:
Then I put the power supply back in place.
The NAS OS saw the new card:
So did Qfinder:
The OS prompted me to upgrade the Ethernet adapter firmware:
I switched network adapters to one of the built-in 2.5 GbE ones and updated the firmware: