I agree with the thrust of you comment though, outside the webbrowser, proper sandboxing a barely used outside web browsers. However, I think the problem is as much social as technical. Every time Flatpak comes up, it mostly gets hostile reactions.
The situation is rather unfortunate. A lot of people believe that Linux is more secure than other operating systems, but in practice the Linux desktop is far less secure than e.g. macOS, iOS/iPadOS, or Android.
And no, you aren't safe because it is open source software. Sandboxing also protects against unknown vulnerabilities in open source software.
If an application uses Gtk+3 or Qt5 then portals will be used automatically for Open/Save dialogs:
https://docs.flatpak.org/en/latest/sandbox-permissions.html#...
I agree with the thrust of you comment though, outside the webbrowser, proper sandboxing a barely used outside web browsers. However, I think the problem is as much social as technical. Every time Flatpak comes up, it mostly gets hostile reactions.
The situation is rather unfortunate. A lot of people believe that Linux is more secure than other operating systems, but in practice the Linux desktop is far less secure than e.g. macOS, iOS/iPadOS, or Android.
And no, you aren't safe because it is open source software. Sandboxing also protects against unknown vulnerabilities in open source software.