Good question on the headless. I actually just got into the VST world myself, didn't know anything about it until a few months ago. "Headless" means the computer has no monitor, keyboard, or mouse. It's just the PC sitting there. There are people who have these really tiny PCs attached to their digital piano out of sight. And instead of using the built in digital piano sound it uses the computer instead. Of course, you actually need a monitor you can plug into and a keyboard and mouse initially when you are setting up your system but after that it can just sit there by itself without much user input. There are also ways to remotely access into these mini PCs from another computer, so if you need to reconfigure things in the future you just do that instead of plugging it back into a monitor and Keyboard and mouse.
The Windows machine I bought is called an Intel NUC. Intel NUC pic It is quite a deal smaller (and cheaper) than even a Mac mini, so that was very appealing to me
My Intel NUC ran a Windows 10 Pro and was fully up to date. Intel NUCs have their own special mini motherboard and BIOS and so I think due to that it gave me serious Input/Out issues. For example, I also had issues with it even recognizing my headphones at first and even now there are issues with it. And yes, the "device is working" screenshot was with the Midi cable not even correctly plugged in. Freaking bizarre. I have another large desktop Windows PC that works perfectly fine and I am sure if I plugged in my MIDI piano to that computer it would be fine.
In any case, I'm returning the NUC and going to be looking at ebay for some used Mac mini m1's.