So what is the “Rigging Tool for Envelope” button that just appeared in Harmony 11.1 in the Deformer Toolbar? It wasn’t in Harmony 11.0 and I can’t seem to do anything special with it. It’s not even present in the online documentation as far as I can tel!
This is ability to surround a shape and deform it is now officially part of new Harmony 12 after the undocumented sneak peek noted by you above.
It’s used to encircle a shape and deform it; used for faces mostly - where precise detail is needed and the Warp effect is not providing the level of control necessary.