The video games industry is filled to the brim with gatekeepers who take their cuts. Valve takes 30%, just for their store. Publishers start at 10%. Your engine might take a cut.
Estimating that Stardew Valley, the big success video game with the lowest overhead bar none, has made 10% profit might be too low. 20%? Might be high.
For whom? The manufacture? It's closer to 10-30% for the manufacture (lower for white label goods, higher for "premium" brands). And it's higher for products that enjoy monopoly status.
For retailers, it's 2-3%, but retailers also get products on loan and negotiate various agreements that help cover the costs of displays, shipping, marketing, and wastage. So even that small percentage margin is skewed a bit.
There's a reason that retailers and food manufactures ("canned goods") were some of the largest American companies prior to technology taking off. It's a highly profitable industry.
Um, exactly the sort of numbers that you're providing. I'm baffled by the question or what possible relevance you thought it had here.
> 10% profit might be too low. 20%? Might be high.
You think an indie game like the one in question is making less on each copy sold than Valve is making on it? That's nuts. If the creator isn't clearing 50% on each marginal unit sold, then something is seriously wrong.