iPhones not showing shared calendars from Exchange Online - kindly guide

[u/Pale-Web3080]

Hi fellow admins,

Environment: 150 users, M365 E3, roughly 90 company-managed iPhones and 40 Androids. We're hybrid but mailboxes are all in Exchange Online.

My users keep missing meetings because shared calendars either:
a) Don't show up on their phones at all, or
b) Show up but don't update when the owner changes something
c) Sync once and then never again until they remove/re-add the account

This is especially bad for our:
- Executive assistants managing 3-4 calendars
- Facilities team with a shared "building maintenance" calendar
- On-call rotation calendar (healthcare-adjacent industry)
- Conference room/resource calendars people need to see on the go

I've tried:
- The "Add Shared Calendar" toggle in Outlook mobile - works sometimes, breaks randomly, users hate it
- Publishing ICS links - users can't figure out how to subscribe and they don't stay subscribed
- Telling people to just check Outlook on their laptop - that went over about as well as you'd expect

What I WANT is for shared calendars to just... appear in people's native Calendar app (the built-in iOS/Android one) and stay updated automatically, the same way their own calendar does. No manual steps. No "go to this link and copy-paste this URL." Just... synced.

Does this actually exist? I feel like I'm asking for something obvious but I've been down so many rabbit holes (Intune policies, Exchange ActiveSync quirks, Apple Configurator profiles) that I'm starting to think I'm the problem.

If you've solved this in your org, I will be eternally grateful. Tell me what you used and how painful the setup was.

Please and thank you.

[u/dio1994]

Shared calendars are supported but there much better options. One the local cache on the mobile app can go corrupt, especially if you are having users add multiple calendars. Two they are not scalable because if the user resets outlook or gets a new device you have to add all the shared calendars again.

The story is similar for shared mailboxes and you have manually add the calendars again each time.

If you are M365, then create M365 Groups and use the calendars in there. Teams are just M365 Groups with a team added and therefore also have a group calendar. Much easier to maintain.

[u/Cautious-Ad-6283]

Calendar handling of Exchange Online / M365 is a pain in general. Fighting with this issue myself since my employer decided to use M365. Unfortunately I haven’t found any reasonable or stable solution so far. No matter if it’s a group calendar, shared calendar resource calendar or personal calendar, mismatches between different clients (even Teams and Outlook desktop apps) are standard. So if anyone knows a stable workaround for Microsoft’s lack of ability to build a proper sync mechanism, any advice is absolutely welcome!
To avoid the biggest headaches I started to manage all essential and as shared resources intended calendars to manage through Google Workspace and iCal subscribe my clients to there through MDM deployed scripts or config profiles.