Elasticsearch Mapping _type is deprecated

All indices seem to rely on setting the index _type field.

Indices created in Elasticsearch 6.0.0 or later may only contain a single mapping type. Indices created in 5.x with multiple mapping types will continue to function as before in Elasticsearch 6.x. Types will be deprecated in APIs in Elasticsearch 7.0.0, and completely removed in 8.0.0.

This doc contains all the useful information which explains why and what you can do to resolve it.

If the _type field is required, I recommend using the "Custom field type" in order to keep the same behaviour. This approach involves adding a new field to your mapping which represents the type.