https://bugs.kde.org/show_bug.cgi?id=351086
This is a feature request posted on the bug tracker from 3 years ago, some users and devs show an interest on this feature request.

The initial idea was to display an handle at the end of the clip for looping like in vegas pro.

Currently the workaround is by copying each individual separately and drag them together. When copy-pasting the clip will be copied to where the cursor is, which is still useful but does not snap to end of clip. When the cursor is on the clip being copied, an error is shown "Can't not paste selected clips"

One of the work around that I could think of with minimal development effort would be by appending the clip to the end when copy-pasting as shown here https://youtu.be/277hd766jVI?t=111