From Setup, enter Report Types in the Quick Find box, then select Report Types.
Click New Custom Report Type.
Select "Opportunities" as the Primary Object for your custom report type.
Enter the Report Type Label and the Report Type Name.
Enter a description for your custom report type, up to 255 characters long
Provide a meaningful description so users have a good idea of which data is available for reports. For example: Report of Opportunities with SalesWings Tags.
Select the category in which you want to store the custom report type.
Select a Deployment Status:
Choose In Development during design and testing as well as editing. The report type and its reports are hidden from all users except those with the “Manage Custom Report Types” permission. Only users with that permission can create and run reports using report types in development.
Choose Deployed when you're ready to let all users access the report type
8. Click Next
As a B related object please select the one which is called "Opportunity Tags" and as an A to B relationship please select the first line "Each "A" record must have at least one related "B" record." Then save.
This should be set-up as the picture below.
Once deployed, your report will be available in "Report", under the category you selected.