Both Apple and Google, and pretty much every other app store (with the cheaper Epic Games Store as a rare exception), usually takes a cut of around 30% from all the sales. Epic has tried to bypass this in Fortnite by adding a store of their own, something Google opposed. This has led to several years in court, trying to settle this case.
In the end, the jury has now decided that Epic has won on pretty much all the instances as Google is in fact running an app monopoly. Google will try to appeal the decision though, so it's not the end of the story quite yet, but Epic says in a public statement:
"Today's verdict is a win for all app developers and consumers around the world. It proves that Google's app store practices are illegal and they abuse their monopoly to extract exorbitant fees, stifle competition and reduce innovation."
The case shares a lot of similarities with the Apple case that Epic lost a few years ago. The Verge has interviewed the Epic boss Tim Sweeney (well worth a read) about this to hear his opinion on Apple, which he still thinks runs a monopoly:
"I think the Apple case would be no less interesting if we could see all of their internal thoughts and deliberations, but Apple was not putting it in writing, whereas Google was. You know, I think Apple is... it's a little bit unfortunate that in a lot of ways Apple's restrictions on competition are absolute. Thou shalt not have a competing store on iOS and thou shalt not use a competing payment method. And I think Apple should be receiving at least as harsh antitrust scrutiny as Google."
Sweeney also compares Apple and Google to Microsoft who was on trial several times for antitrust purposes two decades ago, and actually thinks they are worse:
"I'd say this is the thing that's disappointed me the most with Apple and Google: even at the peak of the antitrust trial against Microsoft, Microsoft was awesome to developers. Microsoft has always been awesome to developers, always being respectful, giving developers a great deal and treating them as partners, you know? And so even as Microsoft was crushing corporate competitors, the developer experience was excellent.
Google and Apple both treat developers as adversaries — they try to attack our revenue streams and prevent us from competing with their products."
We assume Google's loss will end up with more game developers and publishers opening stores of their own on Android to bypass the Google fee. Microsoft is also planning on starting a mobile storefront fairly soon, and we assume this might affect them as well.