There are several things going on. First is you have DEF-Upper_Arm_01.R and DEF-Upper_arm_01.R. You also have DEF-Upper_Arm_02.R and DEF-Upper_arm_02.R. You need to delete both the lowercase arm. Then on your mesh you need to rename the vertex group DEF-Upper_arm_01.R to DEF-Upper_Arm_01.R and DEF-Upper_arm_02.R to DEF-Upper_Arm_02.R. Then you need to rename MCH-Hand_IK_switch to MCH-Hand_IK_switch.L and MCH-Hand_IK_parent to MCH-Hand_IK_parent.L. Then select MCH-Hand_IK_parent.L and MCH-Hand_IK_switch.L in edit mode and right click and symmetrize. That will stop the right arm from following the left arm when you move it. I haven’t tested the IK.
