If Risen generated the same gross revenue on the Epic Games Store, Piranha Bytes, THQ Nordic would keep approximately $3,545,233 - that's $820,616 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $347,077. Epic charges 0% on the first $1 million in annual per-app revenue and then 12% on the remaining amount. On GOG (30% cut), the developer would earn approximately $2,724,617.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.