Microsoft PowerPoint for MS Windows can export presentations (both in the old PPT and the newer PPTX format) to “tagged” PDF. This requires that the user checks the “tagged PDF” option or something similar (e.g. “Best for online distribution and accessibility”) in the export dialog. “Tagged PDF” is the informal name for those features in the PDF standard that make PDF documents accessible for people with disabilities.
A function for exporting tagged PDF also exists in LibreOffice, although it does not work well for PPTX. (PPT and ODP are fine.)
However, I have not been able to find evidence (online) that such an option exists in Microsoft PowerPoint for Mac OS. The features seems to be available in Word 2016 for Mac OS (see Tagged PDF on a Mac at Penn State Uni and this Microsoft Community thread from 2017).
So my question is whether any version of Microsoft PowerPoint for Mac OS provides an option for exporting tagged PDF for accessibility. If this is not the case, Mac OS users will probably need to export PPTX to PPT in PowerPoint and then use LibreOffice Impress to convert the PPT to tagged PDF.