You are using staging server - a separate instance of the ESP Component Registry that allows you to try distribution tools and processes without affecting the real registry.
This component provides a simple C++ API to access Sensirion SHT3X sensors from ESP-IDF applications. It is not ready for production usage, hence the version 0.X.X and the location in the staging repository.
idf.py add-dependency "0xjakob/sht3x-cxx^0.1.0-beta"