ar_orderby has changed to qb_orderby

It never was in the documentation, just one of those hidden gems that you got to learn about.  Basically it allows you to see if  $this->db->orderby() has been set prior to running the query if not then you could set one.

When running print_r prior to running the query on $this->db I can see that ar_orderby has been changed to qb_orderby

How can we now run a check prior to running the db->get to see if db->orderby has been set ?

Many thanks

You can't and you shouldn't.
This is not a gem that you happen to learn about, it hasn't been undocumented for no reason - it's an internal property that you should've never relied on.