It appears the search_api_solr_defaults module was removed from search_api_solr 4.x
https://www.drupal.org/project/search_api_solr/issues/3295726
The step in the README can't be used.
"Enable the Search API Solr Search Defaults module: ddev drush en -y search_api_solr_defaults. (If it can't be enabled due to the "article" content type not existing, you can just create a search_api_solr server manually.)"