If Fran Bow generated the same gross revenue on the Epic Games Store, Killmonday Games AB would keep approximately $6,511,080 - that's $1,427,266 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $751,511. 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 $5,083,814.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.