Old slides with text using those fonts still showed fine. At some point after some update, I could no longer insert new text with the above fonts on my slides. I'm on the 'Insider Slow' update channel for Microsoft Office. I run Mac OS Catalina (10.15.3) and PowerPoint for Mac (version 16.35). So I freaked out when all of a sudden some fonts I often use on my slides (Swis721 BT, a Helvetica variant, and Futura BT for example) stopped working.

People that know me a little, know that I am a bit of a font and graphic design freak.

I still use PowerPoint on my Macbook for presentations (because it supports inline mathematical equations, something Keynote doesn't does, but with an ugly math font and weird baseline).