I don't think that it's logical what you want. When you click on a menu item you want the page to load a different form. So maybe using a pop-up can help you.
Add a microflow button in the top of your form to open the new form will do the trick.
Is not done via the intented menu, but you can create a "custom form based specific menu" by this.
Yes, Samet, you may be right.
Maybe I'm looking at the wrong place. I'm looking for different behaviour for different objects. Navigation to an object now always goes via the menu. I would like to be able to navigate to another object without closing the object that's active. I merely need to do a sidestep and don't want to "clean my desk" as I want to return to what I was doing afterwards.
But you may be right that my approach is not the right one. Any ideas?