There used to be a shortcut to enter the zoom level into that little widget at the bottom left of the document window.

To be precise: that shortcut still exists but it won't work as long as you have the application bar active which contains the new alternative for the zoom field.
If you still want to enter a zoom level by shortcut while having the application bar active you'll need to install a small script and assign the shortut to the script.
You'll find such a script right here.