With WIN 10 it is possible to connect accounts in section Settings > Accounts > Email & accounts, then with UWP APIs it is possible to access related data like like contact and appointments.

Currently with an UWP app it is possible to create appointments to an Exchange calendar with API AppointmentCalendar.SaveAppointmentAsync, instead with an Office 365 calendar the operation is not successfull: is seems that the appointment is created but it is never synchronized with the server.

Thread at https://social.msdn.microsoft.com/Forums/windowsapps/en-US/710e8168-1cc3-4ee9-bf22-45179b0767b1/uwp-app-is-not-able-to-create-appointments-in-an-office-365-calendar?forum=wpdevelop contains original discussion details, then at https://docs.microsoft.com/answers/questions/21557/which-is-the-replacement-of-uwp-user-voice-forum.html it was suggested to me to post a suggestion here.

So please change the Office 365 account so that when it is connected to WIN 10 gives the possibility to business app to create appointments with API API AppointmentCalendar.SaveAppointmentAsync.