If you know the projects you’re looking for, create and save an advanced search report using:
So, specify the two projects in the “In all these projects” field. That will be your report. Save it and it will appear in your sidebar. Share the link and others can do the same. It will be refreshed every time you look at it.
The report will also include subtasks of tasks that are in both projects. If you want to exclude subtasks, you can add that criterion too from the Add filter > More menu.
Larry