It depends. Historically, sandboxing used to protect from takeovers, because computer time and network bandwidth was costly. But today, user information is much

It depends. Historically, sandboxing used to protect from takeovers, because computer time and network bandwidth was costly. But today, user information is much more valuable than computer time. Flatpack partially protects from both attacks on system and on user data, but this protection is not perfect. We should expect that Flatpack protection is (or will be) on par with Android anit-malware protection.