All games which are not explicitly marked with linux support will now by default launch with proton. You no longer need to manually set the compatability for each title, or go into settings to enable proton globally for all non-supported titles.
Pretty nice QOL feature. It's pretty annoying to have to fumble through a few extra steps to enable the damn download button
My take is that this made sense back when Proton was still in its infancy and Valve was working to get the Steam Deck Verified program off the ground. Now we are at a point where Proton compatibility is so high that the expectation is nearly any title will "just work" without any fuss and any game that doesn't is an outlier.
Those games you can force to just run natively via the "Linux Runtime" option. I wish they'd make that UI slightly better.
I wish Apple and Valve would get together and actually make Proton on MacOS a more streamlined experience. the Game Porting Toolkit just isn't where it needs to be -- It feels like it's based on vinegar rather than something that has had lots of compat work done on it.