In traditional Linux distribution everything is installed and blended together from system level program to user level programs. You can install DistroShelf as standard program that gets mixed with system itself.
But on immutable/atomic Linux distributions there is intentional separation between system level software and user level software. System level software is “immutable” and user level software should be installed using some container/sandbox technology. For GUI applications Blufin suggest to install as flatpaks. This is similar to mobile phone way of installing software.
I tried to explain how and why flatpaks are used in System Flatpak Runtimes EOL - #7 by red11.