Select Project 5
Select the fifth project. There is no way to tell what the fifth project actually is. This is likely to be a hold over from early days of Logic going all the way back to “songs”. MainStage is the preferred tool for having multiple songs available for playback.
Studio One now has a “Live Performance” page built in (2020).
Generally speaking it is a bad idea to work with multiple projects open at once. Far too many problems with Logic can be traced to having multiple projects open at once. Caveat Emptor.
In my current test with multiple projects open at the same time the project number appears to be the position of the project in the Windows menu. Project 1 is the first project, project 5 is the fifth.