The days/weeks/months it would take me to add it and fix all the probable bugs it entails could be used to improve the game itself

Making a game multi-platform is improving the game. Massively.

The high level of skill required to write multi-platform games is why most studios don't bother: Windows developers are a dime a dozen but skilled multi-platform developers are rare. Have you got what it takes? Do you have the cojones to step up your programming game? Or are you happy to wallow in the slop with the rest of the Windows game developers?

Also, remember that Linux isn't the only POSIX OS. If you do your porting right, you get to support a shed load of other OSes for very little.

At this point, Linux native is almost more like reinventing the wheel. The people working on the compatibility layers have done so much work to make a windows game feel native that you can almost think of them as cross compilers in a weird gross way

if a bug arises from using proton, it would cause the same issue for users that are forced to use proton.

just click the button that builds for linux. build for as many platforms as you can. if you cant fix all of the bugs due to time, then you'll become a better programmer for your next game and not make thise same mistakes <3

I think the only big benefits that come from having a native Linux port is performance, and compatability (in case running through wine / proton didn't work.) Other than that I can't think of anything else.

is there really an advantage to have native Linux support nowadays?

Yes, performance and consistency.

As a dev, you honestly are asking the wrong question. You shouldn't pride yourself on the corners you're cutting; you should be using them as an opportunity to expand your knowledge and skillset.

You're adding to the pile of developer trash every time you rely on abstraction layers to do your job for you. You're reinforcing an atmosphere where windows developers can get locked-in as much as they want, and it's up to the Linux community to pick up their (your) slack.

In all honesty, I don't have high hopes for your game and you really should consider what I'm saying before you release more trash into the world.