With this function you can tell GameMaker Studio 2 to
activate all instances that have been previously deactivated in a
var _vx = camera_get_view_x(view_camera);
var _vy = camera_get_view_y(view_camera);
var _vw = camera_get_view_width(view_camera);
var _vh = camera_get_view_height(view_camera);
instance_deactivate_region(_vx - 64, _vy - 64, _vw + 128, _vh + 128, false, false);
The above code activates all instances within the room and then deactivates those that are 64px outside of the limits of the current camera view.