As explained in the Helix API reference, https://dev.twitch.tv/docs/api/reference/#get-videos
The get-videos endpoint will only return one video per User ID.
From the reference;
“Gets video information by video ID (one or more), user ID (one only), or game ID (one only).”
However, if you take a look at the reference (linked above) you will see something along the lines of “pagination”. This would be how you would get more than one video returned by using the cursor in the response.