Hello, I am trying to activate my vellum sim only where the falloff is located, in my scene I am using mops but I am not sure how could I achieve this.


Any help is appreciated.

I don't know what a falloff or a mop is, but you can control Vellum with an attribute driving target stiffness, or use an attribute to blend before/after sim positions. You may want to do a little of both if neither one is exactly right.

You need a Stopped Pin to Target constraint. Paul Esteves explains the steps in the youtube video "05 | Vellum Nodes | Pin to Target"
that can be found on the official Houdini YT account.