fancyfiber

Requires the plug-in <a href="https://wordpress.org/extend/plugins/advanced-custom-fields/" title="Awesome plug-in to manage custom fields" rel="ugc">Advanced Custom Fields</a>.
This is a very basic add-on to allow the ability for relationship fields that are associated with a single related item, to be able to add a new 
item to the related item without leaving the post/page you are currently editing. Uses a colorbox pop-up to open the add new post window with very 
limited options.
Usage:
<ul>
<li>Install the plug-in (standard WordPress installation)</li>
<li>Set up a relationship field with only one related item (standard Advanced Custom Field configuration)</li>
<li>Add or Edit a post with the relationship and the new Add New button will show up on the relationship field</li>
<li>Click the Add New button to open Colorbox add new post for the related item</li>
<li>Click the publish button and the new item will be added (or click the X button to cancel) and the Colorbox will close</li>
<li>The newly added item will be available for selection in the relationship list</li>
</ul>
This plug-in was developed for <a href="http://www.tanabi.com" rel="nofollow ugc">Tanabicom, LLC</a> and <a href="http://www.5dspectrum.com" rel="nofollow ugc">5D Spectrum, Inc</a> by <a href="http://hosting.fancyfiber.com/design/" rel="nofollow ugc">Fancy Fiber Designs</a>

ACF Single Relationship Add New

Add a new related item while editing a post, without leaving the current post.

soliddigital

This plugin allows you to use ACF Repeater and ACF Relationship fields as data sources for Elementor’s Loop Grid widget.
Key Features:
<ul>
<li>New Data Sources: Adds “ACF Repeater” and “ACF Relationship” to the Source dropdown in the Loop Grid’s Query tab.</li>
<li>Use Repeater Data: Select any ACF Repeater field from the current post/page to power your Loop Grid.</li>
<li>Use Relationship Data: Select any ACF Relationship field to create a grid of related posts in your Loop Grid.</li>
<li>Repeater Sub-Field Tag: A dedicated dynamic tag to easily pull and display data (text, images, etc.) from any sub-field within your repeater.</li>
<li>Relationship Sub-Field Tag: A dynamic tag to display data from the related posts, such as the post title, content, featured image, and permalink.</li>
</ul>
<h3>Requirements</h3>
<ul>
<li>Elementor</li>
<li>Elementor Pro</li>
<li>Advanced Custom Fields Pro (The Repeater and Relationship fields are ACF Pro features)</li>
</ul>
<h3>Usage</h3>
1. Configure the Loop Grid
<ol>
<li>Add an Elementor Loop Grid widget to your page.</li>
<li>In the widget settings, go to the Query tab.</li>
<li>From the Source dropdown, select “ACF Repeater” or “ACF Relationship”.</li>
<li>A new dropdown will appear below the Source. Select the specific ACF field you wish to use as the data source for the grid.</li>
<li>Create or select a template for your loop item.</li>
</ol>
2. Displaying Data in Your Loop Template (ACF Repeater)
<ol>
<li>Edit the Elementor template you are using for your loop item.</li>
<li>Add any standard widget, such as a Heading, Text Editor, or Image widget.</li>
<li>Click the Dynamic Tags icon next to a field.</li>
<li>Scroll to the “ACF Connector” group and select the ACF Repeater Sub Field tag.</li>
<li>Click on the tag name again to open its settings.</li>
<li>In the Sub Field dropdown, select the specific sub-field you want to display. The fields are grouped by repeater name for clarity.</li>
</ol>
Note that the preview within the template will not display the sub-field data. This is expected behavior because no applicable preview data can be set in Elementor.
3. Displaying Data in Your Loop Template (ACF Relationship)
<ol>
<li>Edit the Elementor template you are using for your loop item.</li>
<li>Your template will be supplied with a standard WordPress Post object, so just create your template as you normally would.</li>
</ol>

Repeaters & Relationships Connector with ACF for Elementor

Connect Elementor Pro's Loop Grid to Advanced Custom Fields (ACF) Pro Repeater and Relationship fields.

ACF Single Relationship Add New vs Repeaters & Relationships Connector with ACF for Elementor