Universities often ask you to send them two or three letters of recommendation. The best way is to ask a professor in whose class you have been successful, had a good theoretical or practical project, or participated in their research activities.
If these professors are outstanding graduates of the university or they are well-known in international scientific communities due to publications, the letter of recommendation you receive from them will be very effective in gaining admission to the university.
If the professor who advise you do not have such features, it is no matter of concern because you only need to be advised by a professor.
Also, if you had been or are working in a research institute and you have contributed to its research projects, if the director of that department is a faculty member, he can write you a letter of recommendation and this recommendation is also valid.