flatpak-preinstall-prototype from home:meisenzahl:elementary-daily project
Select Your Operating System
Add repository and install manually
For Fedora 40 run the following as root:
dnf config-manager --add-repo https://download.opensuse.org/repositories/home:meisenzahl:elementary-daily/Fedora_40/home:meisenzahl:elementary-daily.repo dnf install flatpak-preinstall-prototype