There is a funny moment in the last chapter, when Soske shouts that Rika behaves calmly so that Soske doesn't do it. But if you look at it from the outside, Sosuke also never says anything to Rika (when he found out about Momonga channel, or about Matsuo's debt, and even when he saw the video of adultery). He was always silent and never expressed his opinion, as if giving his silent consent. For some reason, it seems to me that during the school trip, when Rika called Soska to the bathroom, that's when she expected all these words from him. I think Rika is getting a sincere but emotional conversation with her from Soska. Where he doesn't keep silent, as he did before, but asks all these questions that he shouted when he strangled Miyabi. Rika's words "do whatever you want with him" are probably aimed at making Iwabuchi do it so that Sosuke can't hold back anymore. And the result that Rika said that it will be the same, this is this dialogue.
I think that it is after the actions in this chapter that Soske realises that it is impossible to act under the influence of emotions. So to speak, he has matured emotionally here. This will help him defeat Iwabuchi when he tries to break Soska's heart. At this time, Sosuke will look indifferently at Iwabuchi, after which he will say that he deletes all information from Iwabuchi's server.