Protecting application table structures and data

Hi. I am creating a desktop app and am interested in using postgres. I
started this app with sqlite3 which is nice but not multi-threaded so I
have run into its limitations.

I want to install postgres on the users machine as part of the set up
but want the application, if possible, to be the db admin for the
installed pg server. Is this possible?

I am hoping the application can be admin and create the tables and give
the machine's user appropriate access without providing direct access to
admin functions.

Alternatively, is there a way to protect the data structures and data
through encryption to secure the structures and data in a way that
cannot be read by a human? Many thanks.

Regards,
David