PC Gaming

And unlike Apple, it's completely optional to release on steam

Yes, Steam takes a cut as well. But the crux of the argument is the monopoly part. You can distribute your game outside of steam - on other app stores, or sell it directly to customers if you want. On iOS, there is literally no other distribution channel. You have to pay Apple and use their thing. That’s the difference.

The size of the cut is what they use for the appeal to the public to build their social narrative, but legally/economically speaking it's not really the problem. The problem is that Apple effectively forbids developers from having any other mechanism to transact with customers except through their marketplace where they take the 30% cut, hence the lawsuit being about monopolistic practices, not the amount they're charging.

Valve handles things completely differently. Sure, listing on the Steam store requires giving Valve a 30% cut of the purchase price, but Steam doesn't demand a 30% cut of any and all transactions that happen within or related to the game like Apple does. You also don't have to buy a game from the Steam store to load it and launch it from the Steam client. And Proton works with a lot more games and applications than just those on the Steam store.

The fact that the two companies charge a similar price for a single relatively similar business case oversimplifies a lot of how the two companies operate.

I think they probably mean having a launcher that installs on Linux and games that don't need tweaking to run on Linux. Like Steam does it.

Unless you’re talking about Fortnite

Another excellent point.