Four rounds of recruitment

In general, if the recruiter thinks your qualifications are not suitable, it is impossible for you to attend so many interviews. According to your description, you have passed four interviews, and the most important ones here are the last two, one with the boss of the branch and the other with the human resources of the head office, which is enough to show that your qualifications are satisfactory. Why haven't you been informed to join the job so far? It's because you are not the only one to attend the interview. Some positions only need one person and need to be discussed and decided.

My suggestion is that you should take the initiative to call for information in three days or a week at most, and don't waste time.