You are wrong.
The desktop security model is essentially nonexistent. Even if you use Linux, there is no proper sandboxing.
If you take cybersecurity seriously, you should stay away from desktops and stick to mobile devices instead.
As for privacy: all you have to do is switch to GrapheneOS, do not insert any SIM card, enable Airplane mode 24/7, run a VPN, never install Google Play Services or anything from F-Droid/Aurora Store, stick exclusively to FOSS apps and remove as much permissions as possible from them.