Is it possible to make a workflow that can count how many checkbox have been checked?

It’s possible but most simply with script Create a custom field on the record to store the count of checked checkboxes. For each checkbox that you want to count, create a workflow with a trigger on the field update action. In this workflow, create a “Set Field Value” action that increments the counter when the checkbox is checked and decrements it when it’s unchecked.

Thank you. I'll try the suggestion