Help with Shotcut?

You insert a second video track, insert the background video into the lower and the foreground video into the upper track.

You click on the upper video, go to the filter and the “+”. Then add the filter “Deckkraft” or “Opacity”, depending on which language you have set Shotcut.

Then you can adjust the opacity. If you set the time marker to any location, you can see the degree in real time.