@Muslim Abdullayev , Based on my research, I find the ability to synchronize Outlook calendar data to the native Calendar app is now only support with Outlook for Android.
https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/outlook-for-ios-and-android/outlook-for-ios-and-android-configuration-with-microsoft-intune#general-app-configuration-scenarios
For iOS, you can feedback to Intune uservoice to see if we can have this in the future:
https://feedbackportal.microsoft.com/feedback/forum/ef1d6d38-fd1b-ec11-b6e7-0022481f8472
Thanks for your understanding and have a nice day!
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