In the past, I've spoken to many developers about how their games sold on Linux and this time we have information on Slay the Spire to share.
First, we need to take into account that according to the Steam Hardware Survey that Linux only currently represents around 0.82% of the Steam market. Also, this is only on Steam and so it's not counting Humble Store where it's also sold.
Here's the breakdown the developer provided:
95.5% - Windows
4% - Mac
0.5% - Linux
To me, that's a surprise (the developer was surprised too) as that's quite low even for Linux sales. When doing this before (part 5) it did fluctuate quite a lot between 0.6% up to highs of around 16% (although that was a rare one with FLASHOUT 2 in Part 3).
Obviously a big part of the problem is just how many games there are now across all platforms. Even just on Linux, Steam has somewhere in the region of 5,426 games available and that's not taking into account all the bigger titles that can now be played thanks to Steam Play.
Competition is hotter than ever and being a smaller platform, it isn't obviously helping. It's basically the same story as it always has been—increasing our market share somehow is the only thing that will help. The uphill battle remains and will do for a long time, the important thing is to continue to make sure we're worth the time for the developers who do support Linux. Be helpful when issues arise, put up a review for a game you enjoy, tell those developers you enjoyed it on Linux and so on you get the idea.
Slay the Spire is a popular indie game, one with an "Overwhelmingly Positive" user rating from over 20,000 user reviews and it definitely deserves your attention. It's stolen a lot of time away from me personally, it's fantastic.