The app is beautiful! But doesn't seem to work: I see Bibou in the downloads page, but that's it. The "install" button is still lit up, and pressing it again just asked me to download the installer again.

The issue might be that the downloads I have available are ".exe" files. The Linux metadata might be botched?

Definitely looks strange, the file names mention linux but they are exes. You might want to leave a comment on their game page about it: https://andrebertaglia.itch.io/bibou They'll get notified.