Linux for Human Beings.
Ubuntu is a popular Linux operating system for PC / mobile devices, etc.
Developed by Canonical & based on Debian (another older Linux OS) which is known for it's rock solid stability.
Ubuntu is trusted everywhere computing by professionals and common users alike.
The default "App Center" does not support flatpaks (only snaps). However, if you install the GNOME software center with the suggested dependencies:
$ sudo apt install --install-suggests gnome-software
Then you will be able to install flatpaks, debs, and snaps.