How very frustrating for you. I am not familiar with using the applications you mention for video editing. And I work on a Dell Laptop. So assuming you searched the Internet with your question to no avail, it appears that you may need a video editor. I use, and can recommend, the free Shotcut editor as it does work on Macs. (And no watermark.) There is a bit of a learning curve. But by what you describe, it sounds as if either the "Rotate and Scale" or the "Size and Position" Filter should allow you to export in the 16:9 aspect you want. You might want to go to their forum at https://forum.shotcut.org/ first and post your question. I typically get an answer within a day, and often within an hour, of posting my questions. I wish I had a better, quicker solution for you.
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