Perhaps you should look up zero knowledge encryption.

I am considering iPhone as well, since it has “reputation” of being secure.

Which doesn’t mean private.

Pixel+Graphene is a common suggestion.

For real privacy you can’t beat these.

If the app declares it needs location even though it’s not needed (say it’s a text editor) will microg filter it out and/or provide fake data?

What’s “necessary data”?

install slackware