Missing Accept / Decline / Maybe buttons for Outlook invitations on iPadOS

An ICS file is a calendar file saved in a (theoretically) universal calendar format used by several email and calendar programs, including Microsoft Outlook, Google Calendar, and Apple Calendar.  While “universal”, cross-platform issues can and do occur.

If your iPhone running iOS 16.5 works as expected, but iPadOS 16.5 doesn’t, this might suggest that a problem may exist with iPadOS 16.5. However, given that you are attempting to work with a third-party platform (in this case, Microsoft Outlook), you may need to seek assistance from the platform developer - in this case, Microsoft - as they may be aware of the problem and themselves be working on a fix, or be liaising with Apple.

Otherwise, you might seek assistance from Apple Support - who, upon learning that the issue involves Outlook, may refer you to Microsoft.

Should you choose to try, you can contact the Apple Support using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

Are you using the Microsoft Outlook App on your iPad and iPhone, or just using the native Mail App?

To benefit from all of Outlook’s features, you must use the MS Outlook App. If you experiencing issues with the App, your would be best advised to seek assistance from Microsoft Technical Support.

https://support.microsoft.com/en-us/office/outlook-for-ios-and-android-help-cd84214e-a5ac-4e95-9ea3-e07f78d0cde6

Unless you use the Microsoft Outlook App, Outlook-specific functions (such as Calendar integration and invitation acceptance features) won’t necessarily be available to you.

If functions work with your iPhone - and not with your iPad - you may need to seek assistance from Microsoft Technical Support.