I was trying to download this game for my Linux game just now, but when sorting my game list to Linux (on the webpage, in a desktop browser), it doesn't show up.
And when I go to the store page it only shows the Windows and Apple icons.

I think this is an error since there has in fact been a Linux version for a very long time, and it is still available for download when you click on the entry in My Games.

The same thing has happened to Secret Agent. Maybe other games are affected too.