Hi! Sorry for my bad english.... I'm new to LW and I think that my problems with it are all related to my previous experience (10 years) of NLE with Adobe Premiere Pro.
One cool PP feature is that you can easily export part of the timeline simply by moving in and out markers on the upper timeline bar. I tried many times to do the same thing in LW, but I can't manage to do it.
So the practical case is that I have to export, for example, a one minute of video from a longer timeline.

NOTE: problem is not related to the black matte at the end of timeline; I shortly understood how to solve it (and I found it a bit logical, so I appreciate that).

Hi.

In LW it is also possible. Just mark and park the part of your edit and then click the button "pop out tile" or "make copy" (One of them should do the trick). A new edit will be created with only the marked part. Now you can export the new edit.

yeeeah!
It did the trick! The correct command is "make a copy"; at that point, LW creates a subclip that can be exported as usual.

Thak you very much!

This solution above reminds me of one of the main "delights" in Lightworks (for me).

I.e., the ability to quickly create an infinite number of edits.

Besides extracting a portion, and putting that portion in a new edit.
You can also use a new edit to make different scene versions.

Just the other day, i was working on a scene (one edit which contained one scene).
I showed someone the scene.
They then asked me "can't you change this slightly".

Because I put so much effort into version 1, i didn't want to lose those changes.
But i also wanted to see how the person's suggestion might pan out.

So I then quickly made a copy of the edit (whick took one mouse click .
I added the extra cuts that the person suggested to the copied edit.
So i had a version 1 and a version 2 of this particular scene.

We could then look at both versions, compare them, and decide which one worked better.

This process took mere minutes.