That's the problem, VGA is not supported in macOS. There is a link to a DP to VGA adapter in Post #1 that you could use. Otherwise you'll need a monitor with a Digital input, either DVI or HDMI or DisplayPort.
https://www.amazon.com/dp/B017Q8OCSY/?tag=tonymacx86com-20
You must have skipped over paragraph 2 of Step #1. It's easy to do when in a hurry.
Here's the two most important sentences of Step #1
Connect a video cable to your monitor via HDMI, DVI or Displayport.
VGA is not supported so do not connect a cable to your graphics card's or your HP's onboard VGA output. If your monitor only has VGA input then use a
DP to VGA adapter.