I am unable to get the Black Bar Blur function to work on Vegas Pro 18. I have looked at tutorials, and done what they suggest, but nothing works. When I drag the fx effect down to my subject clip, the bars remain black. I'm using Windows 10.
While I don't use that FX so I can't help there, perhaps think about for the future rotating your phone (if that is what you are using) 90 degrees L or R so that your video footage is recorded in TV-friendly horizontal 16:9 and therefore negating the need for the Black Bar FX.
I just added an image to the timeline. It was a vertical image but took up the entire video frame. So I opened Pan/Crop and did a "restore" there which gave me a tall image centered on the screen with bars left and right. I then added one of the "Black Bar Fill" presets to the image and the black bars filled correctly.