Industrial mini PCs will often have 8-32 GPIOs for controlling equipment. Expect to pay a hefty markup for one of these from a name brand, or a moderately reasonable price for a no-name Chinese NUC.

The NUCs you see from e.g. Intel had a "custom solutions header", which was a bunch of common buses on an internal header you could expose with some bios config and wires, including 1-2 GPIOs, but that was it.

I have a qotom box which I use for my firewall and it has a header for GPIO. I think that it might be a singular GPIO, though. You'd have better luck attaching an esp32 over USB to add additional GPIOs.

There are various sorts of USB-based add-on GPIO boards these days, but often you're fine with an ESP or Pico doing some of the low-level work and reporting back via serial or USB HID.

You can always use an AVR or ESP32 as your remote GPIO.

Not typically