No, regular user-space applications have full access to files and other info. However, if you only use the builtin package manager, you can trust that the apps you use are probably trustworthy.
Flatpak apps can be sandboxed, though many apps will come with very loose permissions by default.
The people editing their images in Blender are the same people who edit their videos in Blender lol.
Unlike a car which is bought once and is mostly outside of vendor control once you have it, Proton mail is a service that requires continuous trust in the company since they offer a service. This means I no longer trust Proton as much, which makes me much less inclined to use their services.
I wonder where they got Switzerland from. Looking at the PostmarketOS core contributors, many seem to be from the Netherlands or other European countries. My understanding is that PostmarketOS is almost completely volunteer run, with whoever is willing to contribute.