If Papers, Please generated the same gross revenue on the Epic Games Store, Lucas Pope would keep approximately $16,553,429 - that's $3,047,666 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $2,120,922. 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 $13,072,046.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.