Since I no longer had an icon for Steam in Gnome, I tried to reinstall Steam via pacman -S steam. That didn't bring me an icon in the Gnome overview either, but that was because I had created a separate *.desktop file in ~/.local/share/applications. I removed this and the icon in the overview came back. But now I have the problem that the games I call up via Steam no longer start. For one game, the launcher starts, but then displays the message “Please start Steam first” (Steam is already running, otherwise I wouldn't be able to start the game). Other games bring up the message that no wine-mono is supposedly installed. But it is installed.
A reinstallation of Steam has not changed anything. What can I do?