FYI synergy is free and oss[1] but I would still recommend paying for it because it's priced fairly and I want to support the development behind it. I think synergy is text-book "how to make money with oss."

[1] https://github.com/symless/synergy-core

I, too, tried in vain to buy a decent quality 4k KVM. Oddly the video worked better than the USB mouse/keyboard. (?)

Having failed the KVM route, I, too became a Synergy fan. I don't think Synergy caused the decline of KVM, but it synergy's success is certainly correlated. :)

Yeah, I can see how it might not work for everyone but for my needs it's pretty well suited and become part of my everyday workflow.

I cannot live without this software. I'm using it to control several computers with a wall of screens. My T460p is the server.

Yep, that is what I use for the same usecase. There is really very little point to a hardware KVM at this point.

The remaining use case is when you want to share a monitor along with the keyboard and mouse.