Time lapse portrait images in iMovie

I have imported nearly 1600 time lapse images (RAW format) into iMovie in an attempt to create a short 20 second clip of the Milky Way 'moving' across the night sky. I'm using my 16GB M1 Mac Mini for processing.

However, using portrait mode images doesn't work - wierd up and down motion for each image - so I need to somehow batch orientate all the 1600 images into landscape mode and then create the clip.

I know that there are 3rd party Apps out there, including Lightroom / Photoshop, that can do this. How can I have some sort of assurance that I can maintain image quality and retain as much image information as possible.

Any of you talented individuals out there have an answer to my dilemma please?

Many thanks in advance for your help.