For some reason, if the demo version of a game isn't in your library and you have the full version of that game, Steam won't let you download the demo from the store page. There is a workaround for this but it involves a couple of commands on the command line. This guide is for Windows but it should be a similar process for Mac & Linux (Steam Deck).

1. Open a command line: use cmd.exe or Powershell
2. Run the following command (you can probably copy-paste it): "C:\Program Files (x86)\Steam\steam.exe" steam://open/consoleYou may need to adjust the location of steam.exe if it is installed on a different drive or location. This command will open a special window in Steam where you can give Steam commands.
3. In the Steam command line, run the following command: app_install 2222000Steam should automatically download and install the Loddlenaut demo.

That's it! The "Console" tab in Steam will go away the next time Steam is fully closed and re-opened.