Video editing just IS time-intensive.
For Windows, there’s Movie Maker which is available for free from Microsoft if you don’t have it already. For Mac there’s iMovie, which has more options than Movie Maker, e.g. for layering video so the one on top shows in the rendered movie. To get that for Windows, a few years ago I bought Adobe Premiere Elements, which is a baby version of Premiere, the professional program. Good enough for me.
You do have to separate the audio from the video somehow, so if you open the file in whatever and save the audio only as mp3 or wav (I’m guessing that Shotcut can do this), you can add a different visual in a new file.
A still image rather than a moving one should make a smaller file for a quicker upload to YouTube.
If you want a moving image you can buy stock video from places like
https://videohive.net
https://www.istockphoto.com
and lots more. Read their terms and conditions, though.
Or you can make a slideshow of your own photos, with pan and zoom effects. That takes a long time to put together, however, especially for a session of an hour or more!
A great source of free, beautiful still photos is https://unsplash.com/
For myself, I usually listen to other people’s session videos while I’m cooking or gardening as if it were radio anyway. I’m not watching. A still image would be fine, as far as I’m concerned.