This article is quite biased.
Flatpak can be seen as a framework that allows to sandbox apps, but it doesn't enforce it. Some apps can't be sandboxed totally without modifications.
So the take is more Flatpak apps are not systematically sandboxed.
The "sandboxed" icon issue is not even flatpak, but Gnome Software which is NOT flatpak, which makes me doubt about some other parts of this article as well.
My take on Flatpak is that it's still very much work in progress but does go on the right direction. The core issue is that it's not popular enough to be considered as an official way to package software and a lot of it is packaged by Redhat developers or the community. Which means that a package can be easily abandoned, or modifications in the software itself that would allow proper sandboxing are not happening.
The "sandboxed" icon issue is not even flatpak, but Gnome Software which is NOT flatpak, which makes me doubt about some other parts of this article as well.
My take on Flatpak is that it's still very much work in progress but does go on the right direction. The core issue is that it's not popular enough to be considered as an official way to package software and a lot of it is packaged by Redhat developers or the community. Which means that a package can be easily abandoned, or modifications in the software itself that would allow proper sandboxing are not happening.