As mentioned in the last monthly issue mailings in the distribution of “pay what you want” in Elementary OS included preset Flatpak.
This means that ordinary OS users can now search, browse and install apps Flatpak directly from app store “App Center”.
To cope with situations where one app is available from several sources (e.g., Flatpak, Repo, AppCenter), the list displays a drop-down menu of source. Users just choose “source” from which they want to install, then click Install to get it.
Additionally, app updates, Flatpak installed through App Center are distributed along with regular system updates and apps in the App Center. Individual applications or update method is not required (unlike the Flatpak in Ubuntu that requires the use of Ubuntu Software > Updates).
Support Flatpak in ElementaryOS
But although support Flatpak in elementaryOS is now available by default, support Flathub (Flatpak and other third-party repositories) are not available.
This means that unlike Linux Mint, you can’t browse and install applications available in the Flathub out of the box, no configuration necessary.
To facilitate the users to install apps Flatpak uploaded in the form .flatpakref files from sites such as Flathub, the developer Elementary has created a new app for Flatpak called Sideload:
“Sideload provides a more secure method to help users to obtain isolated applications“, – said the Elementary team, adding that they “recommend that users visit the App Center to obtain high-quality curated apps, created for Elementary OS“.
It should be noted that the Sideload does not support files .flatpakrepo.
In addition, a similar warning message “untrusted app” will appear when users attempt to install an app distributed outside of the set of “curated” store apps Elementary OS.
As this can be annoying, you can disable it.
Elementary OS users who wish to use these (and other) updates, unable to open App Center > Update All to install them.