Had to send a message to Steam support today:
Hi, I bought Samorost 2 over a year ago. My son and I have been playing it on Linux for months. I just opened Steam so we could continue, and now, Steam not only says that it is not installed, but also that it cannot be installed on our computer anymore.
How can we get back the version of Samorost or Steam that we were using a few months ago so that we can continue playing?
I think I'm gonna avoid Steam in favor of GOG when I can. I know this is the way the world is going but having a game working one day, then having it just disappear the next is too much for me.