Difference: what does apple do? It has a store that they check the content on. And provide the small app infrastructure. Also they ask for money for you to upload anything.
What does steam do? They provide a huge infrastructure for games with hundreds of gigabytes and then a workshop for mods and multiplayer and controller support and remote play and a general good service.
The epic games launcher sucks and they don’t even provide half of that and they ask for 25% I think because otherwise developers wouldn’t even consider their shop.