If Hollow Knight generated the same gross revenue on the Epic Games Store, Team Cherry would keep approximately $81,218,156 - that's $10,492,560 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $10,938,839. 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 $64,509,897.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.