I am hoping the Fedora maintainer of Carla is on this list. Carla is not showing up in GNOME Software as available to install since the Fedora package does not container the needed metadata to display it there. It should be fairly simple to fix, in fact I think this 2013 blog post from Richard Hughes explaining what is needed is still correct:

It is basically ensuring the .desktop file has the correct metadata and that there is an appstream XML file describing the application including a screenshot.

Christian