I can't believe that you can't do this, but I can't work out how.
I have Studio 21. I regularly post on Instagram - stories, reels and IGTV to try and publicise my novels. So the aspect ratio needs to be vertical - (9:16), the ideal size is 1080px by 1920px. I have had to resort to making films with pinnacle, then exporting into an on-line programme, such as Veed, to crop it to the correct ratio (and thereby ending up with their logo slapped across the top.)
Surely I should be able to edit in 9:16 within Studio 21?