2 different issues here
you can shoot with your upper body/shooting arm in either Isoceles(2 straight arm) or Weaver(one bent, one straight) with lower part of body in square stance commonly associated with Isoceles stance.
You can also shoot Isoceles with footwork commonly associated with Weaver stance(bladed, boxer type stance).
You can also shoot Isoceles with locked straight arm or with relaxed elbow.
However, in general, you want the weight on the ball of your feet as you shoot with forward lean.
You could also shoot accurately one handed with straight arm or bent arm, as long as sight alignment is correctly maintained as trigger is pulled w/o disturbing the sight picture.