Flatpak 1.12 comes eight months after Flatpak 1.10 as the new stable series that introduces numerous new features and improvements. Highlights include better support for the Steam Linux Runtime mechanism, allowing Steam to launch games with its own container runtime as /usr.
In fact, this new feature allows any subsandbox to have a different /usr and/or /app. Also new is support for TUI (text-based user interface) programs like GNU Debugger, support for Flatpak instances of the same app-ID to share their /tmp or /dev/shm directories, as well as their $XDG_RUNTIME_DIR.