Thank you very much for your reply! Your answer made it clear to me what happens in the FootTrace Function and I actually got the IK to work now with my mixamo character.
So basically the Add 5 + 30 and Subtract 50 defines the linetrace as you said. Now since the foot root of the unreal manny is nearly located at Z:0, this function assumes that the line trace will begin the Z Location where the foot bone is, plus the maximum the characters leg is allowed to be ankled up if the ground is higher.
Same for the subtract but in the opposite direction if the ground is lower.
Thanks to your answer I realized that I had to go from different origins since the root bone (in my case the hips bone, which is the root bone of the feet that gets shipped with mixamo characters) was located at approximately Z:50 so I had to swap the starting position instead of adding 30 to the Z Axis I instead subtracted 50 and subtracted 100 instead of 50 in the second subtract node to get the desired min/max offset respecting my characters root bone.
Therefore the overbending issues got solved and IK seems to be working with these values.
To give an insight here is what my function now looks like:
