Users are reporting a problem in Outlook 2019, 2016, and Outlook 365: the autocomplete list is messed up. It may open upward, not downward, the autocomplete lines may be taller than normal, and you cannot delete entries from the list using your mouse, only the Delete key.
In Outlook 2016 and 2019 the menu is larger (and has initial circles), plus the X is missing to delete autocomplete entries.
This is a bug in the latest Office updates and Microsoft is aware of the problem. The only workaround for Office 2016 and 2019 is to rollback to the previous build. Outlook 365 users can delete the DisableAutoCompleteUpdate value from the registry.
If you are using the DisableAutoCompleteUpdate registry key so Outlook uses the older simple autocomplete list, removing or renaming the value should fix the autocomplete list opening upward.
The key is at
How to revert to an older build
If you want to rollback your office installation, set Outlook / Office to not install updates automatically then use the rollback script to go back a build or two.
Type cmd on the Start screen to find the Command Prompt then right click on it and choose Run as Administrator
Paste this in the command window and press enter to revert to the April 23 build.
"C:\Program Files\Common Files\microsoft shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.13901.20462
|Recent build numbers|
|Release Date & Version||Build number|
|April 29, 2021 Version 2104||13929.20296|
|April 23, 2021 Version 2103||13901.20462|
|April 13, 2021 Version 2103||13901.20400|