Filter product displays by parent taxonomy term
With a view using Products as base_table:


Add a relationship using the taxonomy reference field you're using and do not require the relationship
Add an exposed filter `Content: Has taxonomy terms (with depth)
In the settings, set the depth to the level you want
In the exposed filter itself, you can configure whether multiple values can be selected or not.


But before all that, you need to make sure that only the child terms are selected on the products.