The best practice is to use sans-serif fonts, rather than serif or decorative fonts. Sans serif does not have decorative lines. The fonts would include Arial, Calibri, Century Gothic, Tahoma, and Verdana. The font size should be 24 pt. font for the body text. The font could be larger depending on the audience or page layout.
Open the Power Point Live.
Select the "Review" button from the top.
From the "Review" ribbon select the "Check Accessibility" button.
On the right will be what is found that needs to be fixed.
Selecting any of these will bring you to the issue and highlight it in the slide.
For this example, the Southern New Hampshire University would be the image that is missing alternative text.
Articles to fix these issues can be found at Accessible Features PowerPoint
NOTE: Microsoft 365 (formerly Office 365)