Hi @Friedrich Vosberg ,
You can download the MFCMAPI tool to see if the problematic folders can be found there. If they do exist when you check it using MFCMAPI, you can follow the instructions in the link below to delete these unwanted folders:
Hide, move or delete an Outlook folder via MFCMAPI
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
In case this doesn't help, you can try contacting the in-app support for Outlook for iOS or visit the dedicated forum for Outlook mobile app via: https://answers.microsoft.com/en-us/outlook_com/forum/outlk_mob
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