If Beholder 2 generated the same gross revenue on the Epic Games Store, Alawar Stargaze (Warm Lamp Games) would keep approximately $3,064,539 - that's $722,292 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $281,528. 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 $2,342,247.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.