Necessary, no. Is it highly recommended that you do? Yes.
The film itself is a sequel to Breaking Bad and starts off immediately after the series finale of the show. So not only will it spoil how the series ended, it may also be difficult to understand the relationships of the characters and the significance of the flashbacks in El Camino.
The series Better Call Saul is a prequel to Breaking Bad itself so it doesn't matter if you haven't watched that yet.
