What is the difference between creed ('aqidah) and methodology (manhaj)? And why do some confine Salafism to the necessity of knowing specific shaykhs? And who are the respected shaykhs in Algeria?

Creed (Aqeedah) is what a person embraces and what their heart and conscience are bound by. As for Methodology (Manhaj), it is the path a person takes and the belief they advocate for. It is broader than creed, for every creed is a methodology, but not every methodology is a creed. The answer to who the reference scholars in Algeria are is left to the people of knowledge and the sound methodology concerning it.