Blisteringly fast!
1. Ctrl [E]
to open the timeline editing facility.
2. click the “Streams” tab in the side panel
3. click each audio, video and subtitle stream to de-select those you don't want.
4. click the “Export” button.
That's it!!
Your “converted” copy of the original media file1) will only contain the video track you left selected.
Want to extract just the sound from a video? Extract [only] Audio
[edited]