no flatpak
Erm, no? There are many GUI Software managers with Flatpaks Integration, for example GNOME software or KDE discover
which would just tell you when no update
About every major non diy distro does that
that would be fun and easy to use
For me at least it wouldnt be. If you dont want the terminal, just use something like mint, it has a GUI for everything you need
Also, why have no terminal? Its always a good backup for if you GUI stops working, and if you want GUIs for everything, that dosent mean the terminal has not to be there