PiKVM themselves offer a 4-port switch, which can be chained five times, giving 20 ports in total: <https://docs.pikvm.org/switch/>
It also looks like BliKVM is now making the BLiSwitch: https://blikvm.com/docs/device-guides/BliSwitch-v2-guide/
[1] https://technotim.com/posts/pikvm-at-scale/
[2] https://geekworm.com/products/pikvm-x680
[3] https://www.gl-inet.com/products/gl-rm4pe/