Using classic Outlook for Windows in business environments
In addition to this post from AnotherBug I have found this statement of Diane Poremsky, an independent contultant here in the community forums (Diane Poremsky [M365 Apps & Services MVP]):
"[...]Do you have 2-step verification enabled on your account? If so, try using an app password as EAS doesn't support modern authentication.[...]"
So there is no modern authentication support for EAS at all. It would be nice to get an official statement from Microsoft here.
In addition to this its stated that we, as paid customers of M365 (personal/consumer), have the possibility to open chat tickets within the paid apps. This is right, but the first level support is a real mess. For example:
I contacted them because I added an internet calendar to my outlook.com account (subscription). The Microsoft documentation tells me that this subscription of the calendar will automatically update when there are new events or changes to existing ones within the subscribed calendar. But in fact this subscription does not work. It will only import the current data and will not update. I added it via Outlook.com Web since I want my account to manage the updates (so the exchange server).
The Microsoft support agent first asked me, what browser I use to log into my Mails. Then he told me to just delete all my mobile devices listed in the outlook.com accounts web interface because this could cause synchronization problems...
But its not that the calendar events will not synchronize with the mobile devices (of course they do not from time to time, this is the problem pointed out in this thread) but its the subcription that will not work. So the internet calendar events are not updated from the server of the third party providing the ics subscription.
As this should be handled by the microsoft server (microsoft should ask from time to time if there are new events as they for sure want no push of new events because of the server load) but in fact its not. The subscription of internet calendars just work as import and not as synch...
So, asking here in the community forums will get us no answers and even the support we have because we pay will get us no support.