Surprisingly old thread here but I will add my 2 cents. I just downloaded the 16.1.2418 dmg package. Opened. Dragged SketchUp to the Applications folder in the finder window that appeared.
me: “Thats strange, why was I not prompted that the folder exists?”
Try to open, PowerPC error. Notice it is in the system Applications folder and not the user one. Deleted it, and reopened the .dmg (didn’t even download a new copy). This time I manually put into my user Applications folder. Works fine!
So anyway, I cant quite remember where SketchUp is supposed to live. I know at one time the recommendation moved from the system to the user folder (or the other way around). Regardless, copying to my user Application folder did the trick for me.