Barrier - one keyboard and mouse across multiple computers
Barrier free software KVM that works.

Synergy
Several days ago, I came across Linus Tech Tips' YouTube video on Synergy and how the software enables one set of keyboard and mouse to control several computers. It looks easy to set up and use. However, Synergy which used to be free is now a commercial software. It might be as good if not better than a hardware KVM. At the back of my mind, I wanted to find a free alternative for this experiment.
Barrier
Goggling for an alternative, I found Barrier. Chris Titus has a video about this software. Barrier is a fork of Synergy, open source and free. It was easy to set up and use.
Download and install Barrier
The first step was to download and install the Barrier software for my Mac Mini and Windows laptop. I was keeping my fingers cross because the Mac Mini used Apple Silicon and Windows was running the pre-release Windows 11. They may not be supported fully. Fortunately, all went well. At the time of this experiment, the released version of Barrier is 2.3.3.
Choosing and configuring the server
I decided that the Mac Mini will be configured as the server. This is done by ticking the option "Server (share this computer's mouse and keyboard)". As seen the screenshot below.

Next click on the "Configure Server" button. Then click on the monitor icon on the top right of the next screen. I then dragged the new icon that appeared next to the server. In my case, it was Mac-mini which appears in the middle of the window. I placed the new icon on the right relative to Mac-mini to reflect its physical location.

Next, I had to double click on this new icon and enter the Screen name. This is where I struggled for many minutes until I realised Screen name = PC name and its case sensitive. If the Screen name is not correct, connection will fail.

Configure the client
In the Windows PC, I allowed connection for Barrier when prompted by Windows Defender. To enable the use of the resources connected to the Mac Mini, I checked the box beside "Client (use another computer's mouse and keyboard)"

Usage is simple
When the connection is completed, dragging the mouse cursor to the edge of the screen toward the other computer (in my case the right edge) will cause the mouse to move from the Mac Mini to the Windows Laptop. It does take a few seconds for the mouse to appear on the other screen, but the transfer of keyboard function was always instantaneous. As such, I used the Windows Key / Command Key as a checking mechanism.
Not buying hardware KVM or Synergy
I enjoyed using Barrier very much and it works well enough. As such there is no real need to buy a hardware KVM or Synergy software.