Unable to Add Exchange 2019 Email Account (Ionos) to Outlook (New) on Windows 11

Hello everyone, unfortunately, I am unable to add my Ionos (Exchange 2019) email account to the Outlook Windows app. On Windows 10, it was still possible to manually configure an Outlook account, which worked fine. However, on Windows 11, this option is no longer available, and I can’t revert to the previous version of Outlook either. When I try to add the account by selecting Microsoft 365 - Office 365, Exchange and entering my email address, I always get the error message: We couldn't find a work or school account with that email address. I have already contacted Ionos, but they couldn’t solve the issue either. They mentioned that Microsoft doesn’t allow setting up an Exchange account this way, even though the option is listed in the selection menu. Does anyone know how to fix that? Thank you very much!