If 5D Chess With Multiverse Time Travel generated the same gross revenue on the Epic Games Store, Conor Petersen would keep approximately $2,003,363 - that's $505,233 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $136,822. 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 $1,498,129.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.