Why slide workspace isn't portrait after I change design>slide size>custom> portrait?

Hello Cayce. If the Powerpoint slide thumbnails are in portrait orientation, but the big working white board view remains in landscape, this is usually caused by a rendering delay or a layout change being applied to the little storyboard thumbnails but missing the big working whiteboard view. After selecting Design > Slide Size > Custom Slide Size > Portrait PowerPoint prompts to either Maximize or Ensure Fit, this step is critical, because if you do not select any of the options, the orientation will not be applied correctly to all areas of the layout, and that will typically be overlooked.

In order to fix this, follow the procedure again, select any prompt options confirm, then close PowerPoint and restart it to update the view. If the issue does not resolve, try switching views, such as Slide Sorter or Normal, or check your display scaling, as that can affect how PowerPoint renders the big working white board view.

Here's the reference for full guide: Change the page orientation in PowerPoint between landscape and portrait

Best regards,