"To change from one opened song to another you have to search for it in the menu."
In Studio One Professional, you can have multiple Songs and Projects open simultaneously and can switch between them quickly. The fastest way to switch between any open Song or Project, as well as the Start page, is to press [Ctrl]+[Tab] and continue to hold [Ctrl] on the keyboard. This displays a pop-up list of all open documents.
While holding [Ctrl], press [Tab] to cycle through the open documents. Release [Ctrl] when the desired document is selected. Now, you can view that document.