Flathub sandboxes applications to prevent them from infecting the system if app gets hacked, and lets you control permissions for each app, like microphone, camera etc.

But they are still work in progress and easily circumvented, thus I called them only minor improvements.

The only real issue with Ubuntu is it uses Snap app store instead of Flathub app store.

Flathub has more apps, is faster, and has some minor security improvements. Linux Mint uses Flathub.

HOWEVER, you can add Flathub as additional source in Ubuntu app store app, and use Flathub exclusively.

In that case, no real difference between Ubuntu and Linux Mint other than UI.

You might be thinking about Geocities, it died in 2009. Neocities was inspired by Geocities but is a separate project launched in 2013.