Count of nodes filter in views for a taxonomy with depth
There are several ways to do it, based on how you are going to manage your content.
But for your problem I guess the solution can be this:
1. In Fileds: add Taxonomy term: Name
2. In Relationships, add a Taxonomy term: Content with term
3. Add a contextual filter for Taxonomy term: Name
    3a. Choose 'Display a summary'
    3b. Choose 'Display Record count with link'.

Here is several resources that can help:
Views and node count for taxonomy terms
How to display number of nodes with current term?
Showing how many nodes are associated with a term
Display node count per node reference field