Joined reports get a long-requested refinement in Winter '27: an option to show only the records common to all blocks.
Where
In the Lightning report editor for joined reports, as a new Common Rows Only option. The beta feature must first be enabled by Salesforce Customer Support for your org.
How
With Common Rows Only turned on, a joined report returns only records present in every block. For example, a report joining Accounts and Active Opportunities shows only accounts that actually have active opportunities, instead of listing every account whether or not it matches the other block.
Why
Joined reports previously included records that appeared in just one block, which forced manual cross-checking or exports to spreadsheets to find the true intersection. This option produces the streamlined view most joined-report builders wanted in the first place.