AMD GPUs used to be really good at this. Not sure how well it works nowadays, with generally higher resolutions and thus higher bandwidth requirements. I'd imagine it involves a lot of trial and error with displayport chaining.

Four GPU's with four outputs each would do it.

You'd only need a main board with for x16 physical slots as PCIe x4 would be sufficient bandwidth for desktops.

You're also not pushing the GPU's power envelope, so one beefy or two smaller PSU's would suffice. The AMD WX7000 series workstation cards don't even have the extra PCIe power connectors (last time I looked).

I suspect these are more likely to be two or more machines though.

The main limitation here is number of monitor ports.

Applications that use this many screens aren't running a high level of graphics. Even a bunch of camera feeds aren't going to strain the GPU.

A NASA level computer specs.