Warning: I did only very sparse research prior to this post, so consider me to be a complete noob when it comes to pole targets and/or complex IK chains in Blender.
I could never get a simple pole target setup  (2 arm bones + 1 IK target + 1 pole target) to work.
Every time I try to set up something like that either
- the elbow is moving 90° perpendicular to the pole target or
- if I fix the 90° in some way (e.g. manually fixing the bone roll) it deforms the mesh in the rest position by 90° (the pole target forces the arm to rotate 90° in rest position). Changing the “pole Offset” does the same thing.
The attached rig actually behaves like I want it to:
If I move the elbow IK bone (ArmElbowIK.L) the elbow/upper arm/lower arm bends toward it and the upper arm rotates to match this.´
The main difference to a “normal” pole target setup seems to be that I have a second IK target for the upper arm and the Pole target is actually integrated into the arm.
But I’m a little confused as to why it actually works - this “working” rig is just the result of some try&error with the pole target setup.
Also: How would one set up the same rig without the IK target for the upper arm?
Can anyone enlighten me here?
Thanks & best regards,