I believe both teams need to win this match because Real Sociedad only needs to win both matches if they want to even have a chance of playing directly in the Europa League group stage.
Otherwise, they will have to play the Europe conference League qualifiers.
But, I think Real Betis is not going to lose in their next matches anyways so it will be better for Real Sociedad to just think about holding onto their position.
On the other hand, Cádiz needs the points to stay out of the relegation zone.