How do I upgrade from SketchUp go to SketchUp Pro for my new iPad Pro?
SketchUp Go will give you access to SketchUp for iPad. That means all the iPads that can handle IOS 15 and up.
No distinction between iPad Air or Pro.
SketchUp Pro gives you access to the desktop modeler, eg Windows and MacOS.
… And no distinct versions of the app on Sketchup for iPad. You just have one version on the iPad.
Sketchup Go is just a new Subscription Tier which offers you the iPad app plus the web app.
If you’re not planning on using Sketchup for Desktop and only want to use Sketchup in the iPad, that Subscription Tier is enough. If, besides Sketchup for the iPad, you want to use Sketchup for Desktop in Mac or Windows you need the Sketchup Pro Subscription. If you use it on windows and want to include Vray and other goodies, you can Subscribe to Sketchup Studio.