Use 'sphinx-design' instead of 'sphinx-panels' in the documentation.
More information about how to migrate to 'sphinx-design' here: https://sphinx-design.readthedocs.io/en/latest/get_started.html#migrating-from-sphinx-panels
More information about how to migrate to 'sphinx-design' here: https://sphinx-design.readthedocs.io/en/latest/get_started.html#migrating-from-sphinx-panels