But it seems fairly straightforward who it is.

If it was indeed Collective Shout's pressure campaign that led to Valve and itch.io being told by their payment processors to remove games, then this is how it went:

   Collective Shout -> Mastercard -> Mastercard's head of brand risk (or equivalent role) -> Mastercard's business partners -> Valve and itch.io

We know it was Mastercard who told the payment processors what to do, as the rule they cited to Valve says "in the sole discretion of the Corporation, may damage the goodwill of the Corporation" -- the Mastercard Corporation used its sole discretion to tell payment processors what to tell Valve and itch.io. The payment processors did not decide this for themselves.

Mob bosses order hits, wise guys carry them out. The mob boss has clean hands.

Keep the pressure on Mastercard.

We need to stop these side-channel attacks on democracy. If a government deems some media lawful, you shouldn't get to de-facto ban it by going after publicity-averse private companies that provide hosting, payment processing, etc. https://protectthestack.org/