If Kerbal Space Program 2 generated the same gross revenue on the Epic Games Store, Intercept Games would keep approximately $30,882,133 - that's $5,164,406 more than on Steam.
At this revenue level, Epic's concrete platform fee would be $4,074,836. 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 $24,469,879.
Note: This is a hypothetical comparison. Actual sales volumes differ significantly between platforms, and Steam's larger user base typically drives substantially higher sales.