I don't understand why you are combining tx and RX. PCI, fiber, and the switch/nic are all full duplex, so you don't need to add the two directions together. A dual port nic, even with pcie4, is unlikely to be able to hit 200G ( single direction) unless it's using very large packet sizes.

Since you're limited by the 100G negotiated speed, you nic will never send more than 100G with iperf on a single port.