It's the new version of the ACF Relationship widget from v2.9.0. The new widget is based on Dynamic Posts. It allows us greater future expansion of skins and optimisation of loading times.
The old version is deprecated but not removed.
The ACF Relationship widget allows you to display related Post objects (single or multiple) defined in an ACF Relationship field of the current post.
ACF Relationship doesn't support natively bidirectional relationships, but our widget can simulate and resolve it. It retrieves all posts that are associated with the current post.
For example: if you have associated the Authors to the Books with an ACF Field stored in Books CPT, normally you can only list the Authors in Books single page.
With this Inverted direction setting, you will be able to list all Books associated with Authors on the Authors single page.
ACF Relationship uses the features of Dynamic Posts, so the documentation of some items will point to the common items.
In the query section, you can set the results per page, and order the results by date, post ID, title, meta value, and much more.
You can use the below skin type in the ACF Relationship widget.