Asahi Linux is a project to get Linux running on M-series macs, which has taken a bunch of difficult reverse engineering, since Apple doesn’t really provide public documentation on how they work.
Running Linux means they can run steam games like a Linux machine. This is a pretty impressive landmark in terms of their OpenGL rendering support.
For sure, valid to fear the enshittification of steam. But they aren’t killing proton. Maybe ignoring proton at worst. But Steam has profit motivations for not being reliant on Windows, which has actively been trying to supplant them with the Windows Store for years.
As another separate, profit-motivated company, with a gaming division and a lot to gain from eating Steam’s lunch, Microsoft is not Steam’s friend. Proton is a critical bargaining tool for them, and not having to include windows licenses for devices like the Steam Deck helps their costs too.