UNlink video and audio if necessary via a right-click on either track. You might even lock the audio track. Right-click at the left of the track to see that choice.
Use the chevron to the right of the the split button to split only the video track at the freeze point.
Take a snapshot via a right-click in the preview window. The still will appear under the bin Image tab.
Insert that still at the freeze point on the timeline and drag its handles to the desired pause length.
Freeze.mp4