Outlook Syncing Issues

I work in IT at my company and people come to me for help with their company phones. Recently they had to install a new security protocol (InTune Company Portal) and they can no longer use the Exchange mail app with their work email. (This is important so I'll repeat it: Employees are no longer allowed to connect their work email to the exchange app and MUST use Outlook.) SO no solutions involving Apple's native Mail Exchange, please.

Here is how I have to sync items for them: Settings>Outlook> "Allow Contacts Access"

That's it. There is no way to sync the calendar from this menu. I've updated my iPhone software to the latest version. Still no way to sync calendar. I have gone into the calendar app itself, gone into Outlook on iPhone and on the desktop with iTunes, iCloud, and Outlook. (No, I cannot update to the latest of these because I have not yet been pushed the newest Windows 10 update so please do not suggest this because I highly doubt that is the issue).

Now with iTunes, I go to the iPhone (while plugged in), then go to info. There are three items there: Sync Contacts, Sync Calendars, and Other. Under every single one it says "Your ___ are being synced with your iPhone over the air from iCloud. Over the air sync settings can be changed on your iPhone." I tried to adjust these settings. On the iPhone I went to Settings>General>iTunes Wifi Sync and it led me back to the desktop iTunes under Summary>Options>Sync with this iPhone over WiFi. Checking and unchecking the box did nothing to allow me access to change the "Sync Calendars" or "Sync Contacts" settings under iTunes>iPhone>info.

With iCloud, I managed to find a download that worked with the version of Windows 10 that I have directly from Apple's site. It synced with Outlook (supposedly) and I checked all the sync boxes and applied. Nothing. No change. I waited a while too, because I know it can take a bit to retrieve Outlook Contacts and Calendars. Nada. Nothing. That didn't work and it didn't seem like there was anything more I could do in the iCloud desktop app.

On Outlook, I have tried changing every setting I could possibly find. I've spent an hour on this so far and I can't figure it out. These paths were just on the desktop. On the iPhone I have tried go into the Outlook app, the Calendar app and the Contacts app and under several different places in the Settings. I am just unable to find another place to sync Outlook calendars and contacts because going to Settings>Outlook>"Allow Contact Access" doesn't work for some people. Sometimes it works immediately. Sometimes I have to wait half an hour and sometimes it just never works.

There is also an issue when going to Settings>Passwords and Accounts>Add Account>Outlook. When I try to add a new Outlook account like this, it does not recognize a work email as a valid Outlook Account, or rather, a valid "Microsoft Account" because all the emails are under the same corporate Microsoft Account. So the only account synced to Passwords and Accounts is the iCloud account, which generally most employees with a work iPhone have a separate iCloud account for work. If not, I have them make one before doing any troubleshooting.

This is becoming a very frustrating issue and to summarize here are the issues:

1) Outlook contacts not syncing with iPhone Contacts in general.

2) Outlook contacts not syncing with iPhone Contacts when Outlook contacts have subfolders.

3) Outlook calendars not syncing with iPhone Calendar at all.

4) No way to sync Outlook Calendars from Settings>Outlook on iPhone

5) No way to sync Calendars or Contacts from Outlook with iTunes when iPhone is plugged in.

6) iCloud app not syncing calendars and contacts from Outlook on desktop.

7) Cannot add Outlook Account with a corporate email address to sync.

Details:

Desktop OS: Windows 10 Enterprise v1803 OS build 17134.829

iPhone: Multiple iPhones ranging from 4-X. Software updates range from iOS 10-12

Please no solutions involving Mail Exchange native to Apple as security does not permit the use of this app. Thank you for your time. I greatly appreciate any work arounds.