Have your video on V2 (as you currently do).
Image or color on V1.
Example:
YouTube will upload any resolution you give it. Meaning if you want to upload your vertical video as shown, you can do so. No need to add color or an image to fill the black areas.
If you wish to edit, then export your vertical video for YouTube, then set your Video Mode to Vertical HD 30 fps before you start the project. You can change the video mode during your project but you may need to adjust all of your filter settings.
The Video Mode is located here:
Settings → Video Mode → Non-Broadcast → Vertical HD 30fps
One thing in your screenshot shows your video having an odd frame rate. You may want to convert your video to a solid frame rate. You can do so within Shotcut. It will make a new video file for you to edit with, leaving your original file intact.