Hi @Nicola Soccal ,
Welcome to our forum.
What's the specific version of your Outlook client(File>Office account>About Outlook)? According to my test on my Outlook 2019(Version 2104 Build 13929.20296), the autocomplete list could work normally like below, which seems to I couldn't reproduce your issue:
For your issue itself, did all users in your organization have same issue ? And have you performed any specific operations before it(such as install any update or others)?
Based on my research, I found a similar thread before, which mentioned reverting to an previous version could work normally for them, so in order to avoid the any errors in your last update, it's recommended to follow the suggestions to revert your Office version and re-update your Office to check if it could be helpful to you.
If your issue has any update, please feel free to post back.
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