This is really a shame:
Clips is by far the easiest way of joining together multiple videos shot in portrait mode on your iPhone. It’s much more complicated in iMovie - especially for portrait mode videos.
I used it just this week capturing Pao, my dog, after he dashed out the door and my attempts to bring him home: https://photos.app.goo.gl/gHa88gNrYeJgPa518