Replied by Eagle Six on topic How to fix Vegas Pro 15 Video Render Prevew not Rotate.
Thank You for posting this tutorial.
If I follow correctly, another way would be to set the Project Properties to 1920x1080, add the 1080x1920 source to the track. In Pan & Crop, rotate 90*, then Match Output Aspect, zoom out to fit. Done. That should accomplish the same thing and be a bit simpler and quicker.