There is no such thing as “full security and privacy”. It doesn’t exist and it’s not a useful goal.
Security and privacy don’t exist as absolute values. Things are not universally more or less secure than other things. You need to understand things like the needs of a situation (e.g. you correctly pointing out a modern phone has more use-cases than a landline), who the threats are, and what their capabilities are. Putting a decent password on an iPhone makes it adequately private and secure against my parents. Using a landline is not adequately secure against a government agency. Know Your Enemy!
As for your advice, a quick counter:
FOSS does not imply correctness. In fact, FOSS is great because we know for a fact it has and always will have bugs! That helps us know his much to trust it instead of being a mystery like proprietary junk. So while I personally trust GrapheneOS to do those tasks better than stock ROMs, that line of reasoning is dangerous and historically known to be inaccurate.
FOSS is on the software level anyway, certain adversaries are capable of attacking at the hardware level. Typical scammers aren’t. Who’s your threat??
There is no such thing as “full security and privacy”. It doesn’t exist and it’s not a useful goal.
Security and privacy don’t exist as absolute values. Things are not universally more or less secure than other things. You need to understand things like the needs of a situation (e.g. you correctly pointing out a modern phone has more use-cases than a landline), who the threats are, and what their capabilities are. Putting a decent password on an iPhone makes it adequately private and secure against my parents. Using a landline is not adequately secure against a government agency. Know Your Enemy!
As for your advice, a quick counter:
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