While lots of this is problem of desktops in general, but:

• Linux applications can access your entire home folder, which likely contains most of your data. It can also access e.g. state of other applications, which can be bad.
• While flatpak somewhat mitigates the issues, it is half-baked: permissions are granted directly when you install the app, and user has to manually revoke the permission - Needing e.g. FlatSeal for this is insane as well. With Android/iOS, the user only grants permission when needed, which reduces lots of attack surfaces.
  • Doesn’t too many apps want your home folder access by default? If you think about it, it is a huge security issue - you basically have to trust the app to keep your secrets intact.
  • Mic access can be very problematic, esp when it would be enabled by default if app requests it. Although I don’t know to which extent this would be abused.

Pardon my ignorance, but why people keep trying Linux phones when you can develop on top of open source android version, like GrapheneOS? Linux desktop apps are not exactly secure.