LOL...I wondered just where, exactly, down the garden path you were leading me, old friend.
And a roux is usually made from butter and flour. It adds a "nuttiness" to gravies and other types of sauces. OTOH...one can also use arrowroot, cornstarch, or just plain old flour; however, as you said, these CAN make a gravy lumpy, if not thoroughly mixed well into the liquid.
Madame; if you please, monsieur.
You seem to know your way around the kitchen. I just took up cooking as a hobby. I know a lot about food (you’d be surprised), but I need to develop the skills needed to prepare quality food.