To upload profile picture which will be displayed anywhere when using Office 365. We can upload the picture via Teams.
Open Teams and click the user settings on top-right corner, click the picture location:
A new window will pop up, select Upload picture then click Save A
If you wanted to use Outlook to upload your picture, use Firefox browser (don't use Chrome or Edge since it might be blocked on chromium-based browsers)
Note: This change could take up to 48 hours to be in effect everywhere within Office 365 apps.