When you open the git checkout dropdown and search for a branch that doesn't exist, there is a "Create new branch" and then you have to type the name in again.

I propose an action in the dropdown that if a branch doesn't exist so if I search for "feature/my-new-branch", there will be an item that has the following action:

Create "feature/my-new-branch" branch.

and when you select it, it would generate the new branch and checkout into it.