for many (probably most) ideas and concepts you probably could apply them to macOs with just a few tweaks
but code reuse will be much more tricky in multiple ways. 1st while both macOs and desktop Linux are unixy what proton has to interact with is much more OS specific for quite a bunch or parts; 2nd when proton devs run into some issue with linux OS services/tooling they can (and have) fix the problem upstream, they can't with macOs; 3rd you can do much more "unusual" things with linux, some of them might matter for proton
most importantly proton for mac would be either way a non small money investment and that investment has to pay of in some form
if you only look at game sails I would be surprised if is worth it for either mac or Linux
I my opinion what Valve gains from proton is not earning more money through Linux game sales but a "safety net".
Windows has shown that if they can they would (at least for non enterprise licenses) love to lock down Windows similar to iOS, e.g. allow only their app store and and not allow 3rd party stores on their store. While the last time they tried that it didn't work out and EU is pushing regulations to reduce how much such app stores can be locked down this is still a _sever_ risk for Valve.
So by making large parts of their library "good enough" usable on Linux they always have a way out by providing a in-between of a console and a open Linux desktop which people can run on their hardware or for which they provide hardware ... like the Steam Deck (which is a bit different focused as a handheld but Windows is also not locked down at this moment in time). As a bonus the know-how and code stack they are building allows them to fan out in more areas even if Windows never get's locked down. E.g. they could create an actual console os with a immutable locked Linux core but then use stuff like flatpack-like container technology to still allow using it like a fully free Linux desktop for most use-cases but due to it being locked down at the core they can promise copyright protection and anti-cheat similar to a console to investors and game (weather that is ethical good is another question unrelated to this argument.)
So proton provides value in form of "potential" and "safety net".
But proton for macOs doesn't have any of this benefits. More so then windows macOs is increasingly getting more locked down and you could call Apple "king of the walled garden business strategy".
So for proton for macOS it has to be clearly profitable, which it doesn't seem to be.
And while Apples seems to wanting to get back into gaming on desktop slowly, they also tend to have quite a strong preference for software being developed with their proprietary tools. So while it might seem a good idea for apple to cooperate with Valve short term, long term I would speculate they wouldn't even like something like proton, because that can diverge sells away from their app store and isn't under their control but (Steam being) a part of the "experience" people might start to value a lot.
for many (probably most) ideas and concepts you probably could apply them to macOs with just a few tweaks
but code reuse will be much more tricky in multiple ways. 1st while both macOs and desktop Linux are unixy what proton has to interact with is much more OS specific for quite a bunch or parts; 2nd when proton devs run into some issue with linux OS services/tooling they can (and have) fix the problem upstream, they can't with macOs; 3rd you can do much more "unusual" things with linux, some of them might matter for proton
most importantly proton for mac would be either way a non small money investment and that investment has to pay of in some form
if you only look at game sails I would be surprised if is worth it for either mac or Linux
I my opinion what Valve gains from proton is not earning more money through Linux game sales but a "safety net".
Windows has shown that if they can they would (at least for non enterprise licenses) love to lock down Windows similar to iOS, e.g. allow only their app store and and not allow 3rd party stores on their store. While the last time they tried that it didn't work out and EU is pushing regulations to reduce how much such app stores can be locked down this is still a _sever_ risk for Valve.
So by making large parts of their library "good enough" usable on Linux they always have a way out by providing a in-between of a console and a open Linux desktop which people can run on their hardware or for which they provide hardware ... like the Steam Deck (which is a bit different focused as a handheld but Windows is also not locked down at this moment in time). As a bonus the know-how and code stack they are building allows them to fan out in more areas even if Windows never get's locked down. E.g. they could create an actual console os with a immutable locked Linux core but then use stuff like flatpack-like container technology to still allow using it like a fully free Linux desktop for most use-cases but due to it being locked down at the core they can promise copyright protection and anti-cheat similar to a console to investors and game (weather that is ethical good is another question unrelated to this argument.)
So proton provides value in form of "potential" and "safety net".
But proton for macOs doesn't have any of this benefits. More so then windows macOs is increasingly getting more locked down and you could call Apple "king of the walled garden business strategy".
So for proton for macOS it has to be clearly profitable, which it doesn't seem to be.
And while Apples seems to wanting to get back into gaming on desktop slowly, they also tend to have quite a strong preference for software being developed with their proprietary tools. So while it might seem a good idea for apple to cooperate with Valve short term, long term I would speculate they wouldn't even like something like proton, because that can diverge sells away from their app store and isn't under their control but (Steam being) a part of the "experience" people might start to value a lot.