This is a plugin for OBS Studio that allows you to use the Elgato Sream Deck Plugin from the Maketplace in opendeck. For instructions on how to use, see this page.
This flatpak is an extension for OBS Studio and is therefore not listed on the Flathub website.
To install this plugin you need to run this command in a terminal:
flatpak install com.obsproject.Studio.Plugin.StreamDeckOBSStudioLinuxPlugin