Since the companion app is not able to "see" which clips a user selects in the Final Cut Pro X timeline, we have to use different techniques. There are several approaches to export only the clips of choice:
Apply standard markers on your clips.
Note: markers are only recognized, if they are applied to clips on the primary storyline!
In the clip export settings check "Export clips only with markers". This will exclude clips that have no marker attached.
If you have a long timeline and only want to export a handful of clips from a short section, we recommend to range select (see below) your timeline in order to save rendering time.
To exclude a clip from the export and upload process, select it and press V to deactivate it. As with markers, this only works with clips on the primary storyline.
In the clip export settings enable "Discard disabled clips". This will only export active clips.
Big timelines take long to render. But you can drastically reduce rendering time if you're only interested in exporting a small of section. To share just a portion of a project, you must make a range selection. You can use the I and O keys to set the range start and end points or use the range selection tool.
Note: please make sure that the clips of interest are completely included in the selected range. Partially included clips are discarded.