I don’t know if this is documented or not. It is not in the tutorial video on crossfades and transitions.
By clicking on the boundary between two clips and moving the mouse to the left, it is possible to add a dissolve between the two clips without “time shifting” them.
This could come in handy the clips must sync with something on another track.
Or maybe I’m covering old ground.
Sorry, I must amend my instructions slightly.
Left click on the boundary between the two clips. First move the mouse pointer to the right, then move it to the left past the boundary of the clips. The triangles indicating a dissolve should appear.
Time shifting means sliding a clip along the timeline, thus changing the position of the clip in time. This is one way to create a dissolve, by overlapping clips, as shown in the tutorial video.
The specific way I have documented is not demonstrated in those videos.
The correct way is clearly demonstrated from 3:16 - 4:33 in the video. The “Timeline Trick” as you call it is called a called a Cross-Fade. It’s not a trick, it’s a feature of Shotcut. I was able to easily duplicate it with instructions from the video.
Shotcut 18.05.08
Done correctly, you will get a dissolve. Done incorrectly, it will merely separate the clips and leave a blank interval between them. He doesn’t explain this in the video.
The correct term for that effect is dissolve.