If Tom Clancy's Ghost Recon® Breakpoint generated the same gross revenue on the Epic Games Store, Ubisoft Paris would keep approximately $35,014,016 - that's $5,774,798 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $4,638,275. 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 $27,756,604.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.