It sounds like it could be an Add-in problem.


With Outlook closed, press the CTRL key, keep pressed, and start Outlook by you usual method.
When you see the ‘Your holding down the CTRL key. Do you want to start Outlook in safe Mode?‘:



. . . . release the CTRL key and click Yes.

In the opening dialog box, pick a Profile > OK:



Outlook will look now different – that’s OK – it’s in Safe Mode.

Now click File > Options > Add-Ins > Manage > Com Add-ins > Go:



In the opening dialog box, note all the Add-ins that are checked.



When you have done that, un-check them all and click OK.
Close Outlook, then re-start Outlook normally for a comparison.

If all seems well, go back to the Add-ins and re-check one of the Add-ins that were originally checked.
Close Outlook > Restart normally for a comparison.
Repeat process to see which, if any, of the checked Add-ins is being problematic. It may well not be an Add-in, but this is a diagnostic approach to see if one or several are giving you grief.