There is a new pull request by jnbr against master on the void-packages repository

https://github.com/jnbr/void-packages iperf
https://github.com/void-linux/void-packages/pull/24348

iperf3: update to 3.9.
Adopted.

A patch file from https://github.com/void-linux/void-packages/pull/24348.patch is attached