In Pega Express case types can be created from the "New" link in the slide out panel on the left (there are a few places this same list occurs, for example in the '+Create > New' link in Designer Studio:
In the screenshot shown, there are six forms and this is perfectly fine, but if there are 200 or more forms it becomes unwieldy.
split the forms into groups - and is there any way to automate this in the Navigation menu like it currently is for single level?
use a different type of control here - is that even possible in the Navigation menu?
Give up on the Navigation and create a custom screen to navigate to the form?
The first option seems to be reasonably easy if hard coded, but keeping it automatic so that the user doesn't need to add the form to the menu is highly desirable.
For our current use case (firmwide repository of application forms for all kinds of business processes) it is quite common for the user to not know part of the name of the form they want. If grouping within that menu isn't possible we'll have to create a navigation screen; I suspect we can group within that menu (by custom building the functionality you confirmed doesn't exist) but this might involve hard coding the groups?