And if Flyover isn’t available in your city, like in Viterbo (for context, here’s the current coverage of Street View around the world), you’ll get an ugly, flat, ‘3D‘ satellite view. If 3D buildings aren’t supported, the 3D button shouldn’t be available at all.
I don’t hate new Maps as much as some do, but this observation is spot on. Going into 3D mode without any Flyover coverage means that you see the 2D satellite imagery for the area skewed at an angle to create a 3D perspective. It’s aesthetically horrible and functionally useless.