Not all Manjaro editions have the needed software installed by default, to install software from this application you need to install
web-installer-url-handler package, that is available in Manjaro repositories.
You are advised to use the installer only if you are on Stable branch, as it might not work on others.
You should use the default package manager user interface Pamac
(Add/Remove Software). It does support other package formats,
you might need to install libpamac-flatpak-plugin
for compatibility with additional formats and then activate them under Pamac settings.
There is also pamac-cli
and pacman which support native packages.
Other options to manage third-party packages: For Snaps you can install snapd
and for Flatpaks you can install flatpak there is also
manjaro-cli that supports all package formats.