After googling for “soft moving sculpture,” I found an exhibit of a large icebag which inflates, deflates, and rotates in a very human-like manner.
https://pulitzerarts.org/feature/claes-oldenburg-ice-bag-scale-b-1971/
I also found a kinetic sculpture which uses rigid parts, but gives the illusion of soft movement.
I continued searching for soft kinetic sculptures from these two sites, but had trouble finding any art from soft mediums.
I was interested in the idea of soft architecture, when researching this topic I found this project for a soft transforming pavillion:
Furl: Soft Pneumatic Pavilion
The pneumatic tentacles raise and lower according to environmental conditions.