The ACF Relationship widget lets you 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.
With a custom presentation layout:
Title list, optionally linked
Text editor, to create your own structure. It supports HTML and Tokens;
For a more complete solution, you can use dynamic data of related post to build a complex structure rendered as:
Natural, for the element in the same wrapper;
List, unordered, and ordered;
Grid, display in columns as a grid;
Accordion, as collapsible accordion panels;
Select, a form select that let the user select one of the related posts;
Tabs (horizontal and vertical), useful and the most used
This is the documentation of the ACF Relationship Field: