if you think what certain payment processors are doing with Steam and itch.io is wrong, might it suggest reporting those processors for abusing their market powers to the respective authorities in your country? Japan has already started an investigation, the more countries follow the better
Find the correct authority for every EU country: https://competition-policy.ec.europa.eu/antitrust-and-cartels/european-competition-network/national-competition-authorities_en
For Germany: https://www.bundeskartellamt.de/DE/Aufgaben/Kartelle/Verteiler_Hinweise/Hinweise_Verst%C3%B6%C3%9Fe_node.html
For Austria: https://www.bwb.gv.at/beschwerdeeinbringung
For Switzerland*: https://www.weko.admin.ch/weko/de/home/anzeigen/kontakt.html
For the Netherlands*: https://www.acm.nl/en/tip-off
For France*: https://www.autoritedelaconcurrence.fr/fr/contact-guichet/signaler-une-pratique
* Please double check, as it has no experience with this countries legal system