The ACF Relationship widget depends on specific settings of your CPTs to function correctly. A crucial aspect is how these CPTs are made searchable, which affects their visibility to the widget.
Case 1: Configuring CPTs with CPT UI Plugin
Key Setting: "Exclude From Search"
Action Required: Ensure "Exclude From Search" is set to "false" in CPT UI settings.
Case 2: Configuring CPTs with Other Plugins
General Advice: Look for a similar setting as "Exclude From Search" in the plugin you are using and set it to false. The terminology may vary, but the function remains the same.
Case 3: Configuring CPTs Manually via PHP
PHP Code Check: If you've created CPTs manually in your theme’s functions.php file or a custom plugin, ensure the exclude_from_search parameter is set to false in the register_post_type() function.
Why This Setting Matters
Regardless of the method used to create your CPTs, the exclude_from_search setting plays a pivotal role. If set to true, your posts will not be visible to search functionalities, including the ACF Relationship widget.