as Microsoft changed fo the ne simplified account setup on Outlook 2019 the autodiscover the returned XML will be ignored.
I googled once more today and found the following interesting links:
https://support.microsoft.com/en-us/help/3211279/outlook-2016-implementation-of-autodiscover
https://www.msxfaq.de/exchange/autodiscover/autodiscover_v2.htm
these might help to track down the issue.
plus