3D FlipBook - Is it possible to open the catalog in the slanted view?

You can use ready function for this https://3dflipbook.net/documentation#general-approach :

        ready(scene) {
          setTimeout(function() {
            scene.visual.getOrbit().actions.rotate(null, {dx: 0, dy: -100, state: 'move'});
          }, 10);
          var interval  = setInterval(function() {
            if(scene.ctrl.getPage()<scene.book.getPages()-1) {
              scene.ctrl.cmdForward();
            }
            else {
              clearInterval(interval);
            }

          }, 1000);
        },