About a year ago, the storage extension got a major overhaul. The v2.0.0 release introduced multiple (breaking) changes to the previous version. The current implementation in pystac still uses the v1.0.0 specifications and needs to be updated.
stac-extensions/storage@v1.0.0...v2.0.0#diff-0702e333ed55b8c104ed06e1bdc91b56c7b08a29179e180b39a7359154b08ad3