When running this in Drupal 9, I am seeing:
Unable to parse ....info.yml Duplicate key "core" detected at line 13 (near "core: '8.x'").
Unable to parse ....info.yml Duplicate key "version" detected at line 9 (near "version: '8.x-3.4'").
info-rewrite adds a core key, but this is often already present (though it should now be core_version_requirement). Info files often have version: VERSION. info-rewrite will probably need to update version: VERSION instead of appending a second version key with the actual version.