I don't want the column totals be shown inside Dashboard Gadgets. Is it possible to disable this function without totally deactivating the App?
Yes, a JIRA administrator can disable the 'js-dashboard-module'-Module in the UPM.
I don't see any button in the Issue Navigator when I click on a filter. How can I see the column totals?
Please verify that you are the owner of that filter, maybe you can copy this filter, or contact the owner to enable the calculation for the filter.
