hal09

Thanks for your reply.
However, it is very advanced content for me, so I may not be able to understand everything correctly.

Is my understanding below correct?

[the breadcrumb traffic that I want to create]
TOP page > post X > post Y

-The function of the reference plugin (=”Post Parents”) is only to specify its own parent.
-In other words, in the above example, specify post X in the parent metabox of post Y.
-Specifically, you can set your own parent by specifying the “parent_id” of the parent post.
-However, by default in wordpress, it is not possible to specify the post type of post X.
-In order to make this configuration change, it is necessary to change the part called “wp_dropdown_pages” in the parent_meta_box function.
-Probably it can be done by the above method, but there is no official support.

best regards

Thank you for your support.
I uploaded the Post-Parents directory.
And the “Parent” metabox appeared on the post page.
However, I have additional questions.

question 1
Is the Parent metabox a setting for specifying my parent?

question 2
Parent metabox had only fixed page as an option.
How can I specify a specific post?