If R.E.P.O. generated the same gross revenue on the Epic Games Store, semiwork would keep approximately $40,748,866 - that's $6,621,992 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $5,420,300. 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 $32,318,416.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.