Hoxhunt add-in is missing from Outlook for Mac after switching to new UI, or after upgrading to MacOS Big Sur.
New Outlook for Mac has a completely new simplistic look. For example, add-ins are not visible in the toolbar by default.
As a first step, restart Outlook. Then click on See more items (...) button and try to locate Hoxhunt's Report this email add-in from the list.
(If Hoxhunt add-in is not visible, restart Outlook and try again. If Hoxhunt is still not visible, restart your Mac and try again.)
If you wish to pin Hoxhunt add-in to your toolbar, select See more items (...) > Customize toolbar... and drag Hoxhunt add-in to the toolbar.
(More information on how to customise your toolbar: https://support.microsoft.com/en-us/office/customize-your-toolbar-in-the-new-outlook-for-mac-9add8444-1094-46ee-a540-bcf1d82d98a3)
If Hoxhunt add-in is still not available after restart, please consider switching back to Old UI (turn off New Outlook) until Microsoft releases a new version.
New Outlook for Mac may still contain some experience-breaking bugs. Microsoft is actively developing and improving the user experience, and you can monitor the development and known issues here: