Invalid index options such as "safe" may have been created in the past, before the createIndexes command started validating options more strictly.
In MongoDB 5.0, the listIndexes command more strictly validates index options, and fails when an invalid option is encountered. At this point, the only option is to drop and recreate the index.
This feature request is for the validate command to remove these invalid options as it is validating an index. This would provide a much faster way than recreating the index when fixing an invalid index option.