A lot of people installed malware and, to be honest, nothing really happened. They might have had to change their passwords, but it could have been much much worse if Android didn't have good sandboxing.
I hope that Flatpak and similar technologies are adopted more widely on desktop computers. With such security technology existing, giving every application full access to the system is no longer appropriate.
Why do you need Flatpak for sandboxing?
I really dislike Flatpak for installing multiple identical copies of the dependencies.
Just give me some easier to use tools to configure the access that each application has.