This is a script for Blender 2.9+ that can create a target bone layer on top of your deform bones, quick and painless.

Why?
FBX Export: When creating models for exporting to other software like UE or Unity, it can be helpful for each bone to have its own transform channel. This is achieved by un-parenting all bones from each other. Avoid scaling issues and problems attaching some FX to the hands for example.
Organization: Clear separation of deforms and mechanisms. The latter will only constrain the target skeleton and leave the deformers alone.
Usually not required for pure blender models.

When?
After finishing creating your deform bones and weight painting; before building the rig mechanisms.

How?
Select armature
Load .py file in blender text editor, check & adjust settings at the top
run by pressing [Alt]+[P] or by clicking the triangle button in the editor header bar.
Use "simple renaming panel" addon to quickly add a prefix to all your deform bones, if that's not done yet.

What it do?

• creates duplicate of each deform bone
• renames with chosen target prefix, sets bone relations
• adds copy transforms constraint for each bone pair
• un-parents all deform bones from each other (optional, but kinda important)

For questions or bug reports:
Twitter - @JawSFM