Video has 3min 55sec of "black/empty" in the end -why?

do you have your work area bar visible at the top of your timeline above the timecode ?

if no, click on the settings and show work area bar

adjust your work area bar from the in to the out point of your click by simply double clicking

on the timecode, or simply, if there are unseen extra material drag it from start to end manually

by dragging either of the work area bar handles

make sure the export monitor settings are set to work area bar

In Export Settings panel, please look at Source Range at lower left of window - there are several options in the drop-down list. Default is to export Entire Sequence and the only way this would result in extra material being exported is...if there is extra material in the sequence, meaning even if 1 single frame of video is out there past the end of the edits somewhere, that becomes the end of the program (and end of export), unless you manually over-ride by exporting IN/OUT to points of your choosing.

Either the Source Range is set incorrectly, or you have an orphan piece of media in the timeline past what you think is the end - a single frame won't be visible unless you zoom in a bit

Thanks

Jeff