Just to be clear, regarding the first method that you mention of exporting a clip, do you mean that after copying the clip (so that is in the computer memory), I should then just select the original source (i.e., the whole, ‘master’ clip I have been working on), or will Shotcut put the my new selection into the Source window?
In Shotcut, when you copy a clip it goes to the Source tab. In fact, anything loaded to the Source tab like double clicking on a clip in the playlist will be what’s pasted when you press V in the timeline.
So the “From” drop down menu in Export gives you different options as to what you want to export from. If you are on the timeline then the default option will be Timeline but there are other options like Source, Playlist and if you have range markers set then it will list those. That’s why you can export a split clip from your timeline as long as you copy it which will take it to the Source tab and then you have to pick the Source tab in the “From” drop down in the Export menu.