So it will have good mainline linux support?

Lets be realistic, companies won’t want to make it open source because they think it will lead to a loss of revenue (there is a mindset of “never work for free”). openttd basically led to loss of revenue because now that there is a open source version (even the assets got re-implemented) people that are playing that are not playing proprietary games (including the proprietary original version).

You might argue there is no significant loss, but i don’t think you can prove that especially to the people who own the companies which include pension fund managers who only care about the profits because if they will underperform people will go to some other pension fund or invest in other stuff like real estate.

A source available license is a more realistic option , You get the source code and permission to improve it but still have to pay something to run the game.

That does not mean it fits the open source definition , that you can change it and even sell it

Unclear licensing can be a problem , see for example how cataclysm dda had to remove a tileset due to it.

Doesn’t seem open source, i don’t see i link to something like github or a license.

You might want to post a bounty on it on rysolv (or some better platform if you can find one), That might be a “stronger” or more persuasive signal then posting on social media.