Although no specific reason is known about Sadio Mané's clash with another German player, I believe a decent player like Sadio Mané would not get into a fight so easily. Before the deal with Al Nassr, he was asked by the German media how are you at Bayan Muny, Sadio Mané responded by saying, "You kill me every day, you kill me every day and today you're asking me how I'm doing." It is clear from his statement that he was not good at Bayan Munich so a change of club was very important for him. The deal with Al Nassr will undoubtedly boost his morale. Hope he has a good life at Al Nassr that he didn't have at Bayan Munich.
Sadio Mane has achieved a number of trophies at club level during his career with Liverpool, at Bayern Munchen Mane is actually not so bad with 38 appearances and 12 goals. However Tuchel expectations could not be met with Mane performance like that, a series of injuries and changes in coaches prevented Mane from adjusting to his game in the Bundesliga and slowly affecting his performance.
Al Nassr came to take advantage of this opportunity to bring him to the SPL, transported with a dowry of 37 million Euros and given the fourth biggest salary in the SPL is not a bad thing I think.