If Outlook won't open or running slow, you can try opening it in safe mode, which disables add-ins and isolate if there is any issue with the add-ins.
Please follow the steps below to open Outlook in Safe Mode:
Right-click the Start button at the bottom left, and click Run or Press Windows Key + R together on the keyboard to bring up the Run prompt.
In the Run box, Type Outlook.exe /safe, and click OK.
If you have multiple profiles in Outlook, you will get a prompt to choose the profile you want to open in Safe mode.
Click OK, then Outlook will open in Safe Mode.