Just out of curiosity, I finally managed to run the native Linux version :D
I did --appimage-extract as it suggested, which extracts the contents of the contained virtual filesystem (now I see how it uses FUSE internally!). It couldn’t find the extracted libraries, however, since they are in this extracted location and not in the standard paths, so I either had to use LD_LIBRARY_PATH to temporarily add the library paths or LD_PRELOAD to simply preload all the libraries from this AppImage (I chose the latter). After that, the game launched!
