How to access desktop Gmail on iPad Pro?
Sure you can, you can use any browser available. Just realize that all browsers on all IOS devices use the same layout engine: Webkit. It's an Apple thing and hasn't changed since Apple allowed third party apps.

As for the keyboard shortcuts, it all depends on what the browser supports. Safari doesn't allow you to customize much. But there are other browsers (Chrome, iCab, etc.) that allow more customization and may allow you to set the User Agent to a desktop version of your favorite browser. Beats me if they will then support the whole suite of Gmail keyboard shortcuts, you'll have to test that.

And you can save any bookmark as an icon that opens that browser with that web address. In Safari go to the page you want to save. Tap the sharing button and select "Add to home screen," voila icon on your home screen. Most browsers let you do this as well.