Problem with 10 gigabit network

1 I have a switch CRS317-1G -16S +
2 Three servers
3 Everywhere installed network card Intel X 520AD
4 cable SFP/SFP+ MikroTik XS+DA0001

When I run the utility iperf3 in single-threaded mode. I have a speed of only 3.5 Gbps.

But the problem is that veeam works in single-threaded mode and the speed is needed 10 Gbps.

How can I increase the speed?

The switch is configured by default

In that case you have to check if server processor (threat) goes 100%, if yes is not problem of Mikrotik Switch.
Then check configuration in Mikrotik Switch, do you have just one bridge on hardware offload or you have many and traffic goes from switch cpu?

You sure about that ? Or are these different products?

https://helpcenter.veeam.com/docs/backup/vsphere/enabling_multithreaded_transfer.html?ver=120