Yes, actually flatpak triggered some interesting projects that are going beyong flatpak now: - pipewire for audio/video stream management that allows sandboxing - xdg-desktop portals to integrate the sandboxed apps in the host desktop environment and operating system. It's what allows the host DE ui to grant permissions (like reading/writing a file, accessing screen share, etc...)

It will depend how an app has been packaged, but when well done the sandboxing is invisible.