If Crusader Kings III generated the same gross revenue on the Epic Games Store, Paradox Development Studio would keep approximately $101,104,334 - that's $12,300,394 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $13,650,591. 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 $80,328,448.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.