Outlook for Mac

Outlook may be working normally. And remember, the app and the data are two different things. If you "deleting and reinstalling Outlook for Mac" you likely did not touch the Group Container where all of the data is being held (~/Library/Group Containers/UBF8T346G9.Office). I suspect you removed the items from /Applications and then reinstalled. That action, using the standard installers and a likely drag to Trash, did not impact your data. However, I don't think you need to delete the data as I believe you simply minimized a number of windows.

From your screenshot, the items with the ◊ icon are minimized windows. The one with the √ is the active window. The ones with no icon are visible but not the active view (only one window can be active (top-most).

From your contextual menu, select each of the items with a ◊ icon. Does it appear? If so, close that window. If not, does it change from a ◊ to a √ in the list. If so, try using Command W to close the now "active" window. Repeat this until you have closed all of your minimized, duplicate windows.

Outside of this, and assuming you are using Outlook because you have an 0365 account and all of your data is in the cloud (you are not making use of the On My Mac folder), then you can always delete the account and add it back. The beauty of everything being in the cloud is that if local corruption occurs, purge the local store and allow everything to come down fresh from the cloud in a new DB>. From your screenshot, the rebuild sounds like the sledgehammer approach while may need a few finger taps to close minimized windows.

Hope this solves it,

Reid

Is it the Microsoft Outlook app or an Outlook.com account in Mail?

If it is the Outlook app, you should ask Microsoft.

If the latter, remove the account from Internet Accounts, go to the web portal and confirm the mailboxes do not exist, then add the account back to Mail.