If Evidently's save_html fails, check how you installed it: use pip rather than the old conda builds, or upgrade to 0.2.4+, where the conda package includes the HTML resources. The missing nbextension error is really a missing-resources error.

Context: Evidently issue #496 (closed): report save_html failed without nbextension installed. Maintainer Liraim identified the cause: the native conda package of evidently was missing the embedded HTML resources. Installing from PyPI worked. The reporter confirmed pip fixed it, and the maintainers updated the package build script so conda installs have worked since 0.2.4.