Reading Order
Screen readers interpret content elements in the order they were created for each slide. You may need to review and update the reading order so that content flows in a logical order. To view the reading order go to the Home tab and select Arrange > Selection Pane...
This will open the Selection Pane.
The Selection Pane will show all the content areas of the slide selected with the first content displaying at the top. To change the order, click and drag content as needed. Titles may need to be moved to the top so they are read first.
Repeat this process for each slide.
Note: you can hide elements in the Selection Pane by clicking on the eye icon for the element.
This can be useful if you want to hide any elements such as title. Screen readers will still be able to detect this hidden content.
Reference: Make your PowerPoint presentations accessible to people with disabilities by Microsoft.
