If Euro Truck Simulator 2 generated the same gross revenue on the Epic Games Store, SCS Software would keep approximately $229,725,308 - that's $23,993,210 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $31,189,815. 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 $182,640,586.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.