I solved the issue:
This is a cross-application problem resulting from MS Office's monolithic integration of AI. I turned off connected services because co-pilot was just too intrusive on powerpoint, and there's no other way to turn it off. This apparently disables the focused inbox on Outlook.
So I guess we're forced to choose between a crappy UX in Outlook or poor productivity in Powerpoint. Which is too bad, because there's a high-value use case for Copilot, it's just not "every moment the app is open", especially since Copilot is a massive resource hog, and when it's running everything is 10-50x slower - and I mean everything, since just typing text into a textbox lags my rather slow typing speed.