This seems like a very simple question and I am inclined to treat it as a trick one, but I will be trusting and try to answer it.
The difference is huge.
A package manager installs, removes, updates etc. components of the OS. It manipulates files in /bin, /sbin, /lib, /usr and so on.
In Endless, the root filesystem is read-only and immutable. It is not possible to modify any of the files provided with the OS in any way, including all of those paths above and others.
Flatpak apps are containerised and all of their components are within the app bundle, typically in `/var/lib/flatpak` I believe. (I am not a GNOME user and don't use Flatpak much, but I have a couple of Snap apps installed.)
Nothing goes anywhere else or is allowed to install dependencies etc.
Think of it like a Smartphone. Android and iOS are both *nix OSes. The entire OS is essentially a single image, kept in Flash, and booted into RAM each time you turn on. The user can't change it in any way. Apps are kept in a separate chunk of flash memory and they can't change the OS. OS updates are a single big file that updates the entire OS partition in one operation.
It's a little bit like booting a Live USB with a persistent storage file: nothing can change the SquashFS, but you can add your own files and have them survive a reboot.
Endless works the same way. It is comparable to Red Hat Atomic Workstation, Core OS, Chrome OS, and SUSE MicroOS.
The difference is huge.
A package manager installs, removes, updates etc. components of the OS. It manipulates files in /bin, /sbin, /lib, /usr and so on.
In Endless, the root filesystem is read-only and immutable. It is not possible to modify any of the files provided with the OS in any way, including all of those paths above and others.
Flatpak apps are containerised and all of their components are within the app bundle, typically in `/var/lib/flatpak` I believe. (I am not a GNOME user and don't use Flatpak much, but I have a couple of Snap apps installed.)
Nothing goes anywhere else or is allowed to install dependencies etc.
Think of it like a Smartphone. Android and iOS are both *nix OSes. The entire OS is essentially a single image, kept in Flash, and booted into RAM each time you turn on. The user can't change it in any way. Apps are kept in a separate chunk of flash memory and they can't change the OS. OS updates are a single big file that updates the entire OS partition in one operation.
It's a little bit like booting a Live USB with a persistent storage file: nothing can change the SquashFS, but you can add your own files and have them survive a reboot.
Endless works the same way. It is comparable to Red Hat Atomic Workstation, Core OS, Chrome OS, and SUSE MicroOS.