When downloading the offline installer files for Windows there are 2 strange files.
surviving_mars_marsvision_song_contest_evans_249143_32867.sh
surviving_mars_mysteries_resupply_pack_evans_249143_32867.sh
What are these files and how do I use file extension .sh?

to my understanding these files are for Linux, you can check foryoureself next time when you dn on the middle left side System: windows click on check mark under win ,Linux, mac. and you will see these file in there.

Why do they show up when Windows is the selected OS?

asked gog

I did...

I was checking the forums and saw that this game specifically seems to have some bugs with the OS selection (or so I understood). Users from an older Linux distribution seem to be getting the installer from the newer one. Maybe someone in GOG did a cock up... You might want to contact them. I usually get a fast reply when I need them.

Because I use Linux, I have no idea how Galaxy works, as we are not blessed with a version for Linux, but don't you have a "download offline installer" option there or something similar? (again, got no idea, just a wild guess....).

Good luck tho!

I don't use Linux or Galaxy. It's either download through my browser or with GOGrepo. Those files are showing up in both. So I figure they must be flagged as Windows files somewhere.