Could someone please help me out? I have purchased a windows version of the game. Can I get a refund?

Also, Is there a version compatible with Mac?

Please place links in answer if you can thank you

You don't buy specific versions of games here. You just buy the game (same as on Steam). There's no reason to get a refund because you can just download the Mac version. If you're using Galaxy there's no other option anyway, otherwise select the correct OS before downloading.

Could you help additionally please. I down loaded the game because it said that it was compatible w/my Mac version Catalina 10;15.1

It said that the file could not be opened because windows apps are not supported?

How do I get to the page if at all that has the Mac compatible Kerbal?

Thanks

I would recommend using the GOG.com website rather than the Galaxy client. Simply log in to GOG.com and click your user name at the top of the page in the black menu bar. Click the game you wish to install. On the game's title card that appears, right under the game's title, make sure your "System" is set to "Mac". Then scroll down to the section titled "Download Offline Backup Game Installers". Click the installer listed there, and you should get the Mac version.

Not sure why GOG is recommending you download the Windows version, but Kerbal Space Program does indeed have a Mac version. So you just need to give GOG a good swift kick in the pants and explicitly tell it that you're using Mac OS.