That functionality (cross-project reporting) is available only if you have the full ALM edition. If you have the Enterprise or Starter or Essentials editions then the functionality isn't available.
If you have the full edition, you also have to have access, as a user, to each of the projects you want to include in the report.
If you have all that, then the place you see the option to pick multiple projects is when you are in the Dashboard module, in Analysis View, and you use the Graph Wizard to create a new report.
If you have the full edition, you also have to have access, as a user, to each of the projects you want to include in the report.
If you have all that, then the place you see the option to pick multiple projects is when you are in the Dashboard module, in Analysis View, and you use the Graph Wizard to create a new report.