The concept is to make a panel layout that emulates the workspace (screen) layout. While testing I have set all the buttons to be the Splash Screen operator.
An image of how this looks for five default workspaces Animation, General, UV Editing, Compositing and Scripting
so apart from nesting the layout is pretty much
for a in context.screen.areas: layout.operator("wm.splash", text=a.type)
At a loss to explain why some of the buttons display the button text as a tool tip, and some don't. 'OUTLINER' and 'PROPERTIES' always have the tooltip. Sometimes one 3d view in animation does and the other doesn't.
Any operator can be substituted for "wm.splash" and shows the same behaviour.
The only reference to "tooltip" in
UILayout is for template list which I am not using.