A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
I'm working with another user (on Reddit in this case) with a similar-sounding problem.
In his case, it's a free font that Windows File Explorer recognizes as having Installable embedding, but if you use the font, save with PPT set to embed all characters, then uninstall the font from the computer, you don't get the correct font when you open the file again. The file itself grows enough to suggest that the font's embedded, but PPT won't use it.
But also in Win File Explorer (going back to when the font's installed), there are a lot of missing attributes: category and several others are missing, leading me to wonder if PPT is refusing to use the embedded font (which would also mean installing it permanently in this case) out of an abundance of caution.
You might want to check the font attributes for your font, see if this rings any bells.