Hi @mr zack ,
Welcome to Microsoft Q&A!
Before going further, please kindly accept my sorry for the inconvenience caused by Outlook.
As I know, the situation you mentioned above is related to a recent known issue, please check: Autocomplete is messed up in Outlook (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 order to use the older simple autocomplete list, it's suggested to disable auto-update and revert your office version via command like below:
C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe" /update user updatetoversion=16.0.13901.20462
You could also keep an eye on the updates in this document to know the latest progress of this issue: AutoComplete list scrolls off the screen in Outlook.
Hope this can be helpful.
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