Nobara does not ship the Fedora flatpak repositories. Instead we ship the official Flathub and Flathub-beta repositories, enabled by default.
For flatpaks, you can use Bazaar installable from the Nobara Welcome App --> Recommended Additions, or any other flatpak store you prefer (Flatpost, KDE Discover, GNOME Software). To update from terminal:
flatpak update -y