What are the monthly salaries of cashiers and clerks in France?

Caissier/vendeur are both revenue of SMIC.

How can French masters be professional counterparts in these jobs that do not require academic qualifications?

If you need a professional counterpart to change jobs, then honestly find a job that requires a French major. After all, the examination of work permit requires not only professionalism, but also salary level and educational background required for recruitment, which correspond to your qualifications. In DIRECCT's eyes, a job as a supplier of bac+5 is a job with a high degree of education and a low degree of education, which is "unfair competition" and must be rejected. I have a friend who is a graduate student in biology and has come to apply for an undergraduate position.