Like what the old software centre did before Xenial, it showed a notice that the same software is already installed but with a different version (older or newer). This notice could be shown in the Details section of gnome-software, like the notice that is shown when installing an unconfined snap.
And if a third-party software already exists in the repositories (installed or not), it advised the user to install the one in the repositories (safer) instead of the third-party one, and showed both versions.
Like what the old software centre did before Xenial, it showed a notice that the same software is already installed but with a different version (older or newer). This notice could be shown in the Details section of gnome-software, like the notice that is shown when installing an unconfined snap.
And if a third-party software already exists in the repositories (installed or not), it advised the user to install the one in the repositories (safer) instead of the third-party one, and showed both versions.