Single KVM that "Swaps" Monitors between two different laptops - The Cheap Way

 I wanted to have my two external monitors connected to two separate laptops, but noticed that when I switched KVM inputs, it would disable the external monitor for one laptop, and enable the other.

My preference was to use my larger monitor as the "primary", for whichever laptop was in-focus on the KVM, but my smaller monitor would still carry the signal from the second laptop.

Off the shelf solutions exist which require extensive configuration, are limited in their ability to perform in all scenarios, and are expensive. I saw another way.

The secret sauce is two of these: https://www.amazon.com/dp/B082CXZP71

These are HDMI splitters, which create two identical copies of a single HDMI input.

The pivotal part is that you get a KVM that has two inputs *per PC*. For my scenario, I wanted only one external monitor per-laptop, for two laptops, displayed on two screens, with the display "flipping" alongside the KVM switch. https://www.amazon.com/dp/B0GQT8SZ11 This has changed over time... please make SURE you choose the one that has two or more monitors per PC. I also prefer the one with the remote wired switcher.

The rest is just a pseudo-Hafler circuit made from HDMI cables.

Laptop 1 Dock > HDMI Splitter 1 > KVM PC1 Input A

Laptop 1 Dock > HDMI Splitter 1 > KVM PC2 Input B

Laptop 2 Dock > HDMI Splitter 2 > KVM PC1 Input B

Laptop 2 Dock > HDMI Splitter 2 > KVM PC1 Input A

For me this required eight HDMI cables, an increase of six HDMI cables versus the prior setup.

The upshot is I can now switch my KVM, and the "primary" laptop appears front-and-center, while the secondary laptop remains visible on an external monitor. Once I 3D print the TouchID units, I'll be able to hide a literal rat's nest of cabling, making this a pretty elegant setup given the capabilities. When that happens I'll try to minimize the HDMI lengths between the splitters and KVM, and probably label everything for troubleshooting/upgrade purposes.

On my two Macs (one M2 Pro MBP 16", one M5 Air 15"), I did have to Arrange both iterations of the outputs, one for KVM 1 and one for KVM two, to make sure the mouse/window movement felt fluid. But now the settings are saved and usability is great!