Instead of add_action( 'admin_init', [ $this, 'aa_admin_page' ] );
Try: add_action( 'admin_menu', [ $this, 'aa_admin_page' ] );
Edit: And all instances of $this->$foo
should be $this->foo
Instead of add_action( 'admin_init', [ $this, 'aa_admin_page' ] );
Try: add_action( 'admin_menu', [ $this, 'aa_admin_page' ] );
Edit: And all instances of $this->$foo
should be $this->foo