This is where you decide what to leave in your video and what to cut out.
I created a sample image of 1920x720, and used the Vertical Video Mode as needed for YouTube Shorts and Facebook Reels.
The first track I made a yellow color to indicate where video would be black.
Applying any filter to force the height beyond 720, going to 1920 will result in distorted video. You would have to decide what portion of the original video would be visible.
Here is an example I made from this image.
This is just for comparison to the video resolution you want, to what you are working with.
To edit a different resolution to a Vertical Video Mode, you will need the filter
Size, Position & Rotate. I did try Crop: Source with Center selected, but it left thin letterboxing at the top and bottom.
You could limit the size to 720 with Size, Position & Rotate for no distortion. Then decide which of the left & right would be visible.
An alternative would be using the filter Blur: Pad
Many different options in Shotcut to make a video.