Ask five companies what a QA role does and you'll get five different answers. In one team, they do manual testing and non-functional testing. In another, they write automation scripts and maintain DevOps. Somewhere else, they could even be named differently. That's why I will not attempt to classify the structure of QA based on titles, but rather based on skills and family of duties. The aim is to give you a blueprint of the areas and what they do, and the associated skill set, so that you can plan your career growth and target specialization or maximum exposure.