Boycotting itchio empowers groups like collective shout even more, you show that them weaponizing payment processors can take down any storefront they deem to have content they don't see as appropriate.
Unfortunately going after payment processors is hard, it will take major law changes to break up the duology or create restrictions to what payments they must accept or having another big contender like crypto which I'm not a big fan of but does eliminate the control the big payment processors have over what people are allowed to buy.