If you have an existing PowerPoint file, you don't have to start from scratch:
Upload the PowerPoint to Google Drive and then open it in (convert) Google Slides.
See animations below and resize slide(s) to your preferred dimension.
If you have multiple slides (representing a story/theme) that would be better viewed as a video:
Upload/convert a PowerPoint or create a new Google Slides.
See animations below and resize slides to the video dimensions.
Download as a PowerPoint file.
Open file in PowerPoint.
Save As an .mp4 file. It will loop in the video (blue) section as shown above.
Download the slide as an image:
If you have multiple slides (representing a story/theme) that would be better viewed as a video:
Download as a Microsoft PowerPoint file first.
Open in PowerPoint.
Save As an .mp4 file. It will loop in the video (blue) section as shown above.
Use the Custom Size button and select the dimensions you need!
Download the design as an image: