How is Proton a technology/library/sorftware? I got the impression it's just a preconfigured Wine, but not an actual implementation. Sorry if I'm misinformed.
And _if_ that's true, I'm sad about the credits not going to the Wine team.
Proton is Wine + DXVK + d9VK + custom patches.
The 'secret sauce' is actually 'Steam Play' which is the automated wrapping, configuration and execution of Proton wrapped games without the user having to do anything (other than a confirmation box to confirm that a compatibility layer is being used).
The Steam Play component turns it from a 'nice meta-distribution for wine' into 'killer quality of life improvement'.
How much of this is open source? I'd expect everything, including the per-game details?
(Not asking you to do research on demand, just in case you already know...)
Steam Play is part of the Steam client, so is proprietary. ProtonDB isn't open source but does data dumps to github regularly [3].
[0] https://github.com/ValveSoftware/Proton/
[1] https://github.com/doitsujin/dxvk