Okay that's really an important information. So it changed after a year of using it and just recently there was an update to the New Outlook for Windows that changed how it interprets iCalendar (ICS) invitations for non-Microsoft accounts (like Gmail, IMAP, Yahoo, etc.), which seemed related to the buttons disappearing. This actually is a known regression and has been reported to feedback hubs already.
In the meantime, until Microsoft re-enables the RSVP buttons just accept via your provider’s web calendar (e.g. Gmail → Calendar.google.com) or switch back to Classic Outlook where the old iCalendar parser still works.
- Toggle off “New Outlook” in the top right corner.
- Your data/account settings remain intact.
You can also submit a report, the more reports, the more it helps push the fix faster.
- Click Help → Feedback → Report a Problem
- Mention: “Meeting invitations for non-Microsoft accounts (e.g. Gmail/IMAP) no longer show Accept/Tentative/Decline buttons since late Oct 2025.”