(Ésta es la respuesta en inglés, la respuesta en castellano la encontrás aquí)
As of now that information is not shown in InvicePlane, and the only way to get the total number of invoices of each type is through the option “Invoices → View Invoices”. Click the button of the type of invoice (all, submitted, etc.) you are interested in, and then click the button
to go to the last page. The number of invoices of that type is shown at the end of the URL, for instance,
Using this same approach you can consult too the number of quotes, clients, etc.
I will open an issue in the developers portal to implement that enhancement in a future version.