What is the difference between core.entity_form_mode and core.entity_form_display? I'm trying to learn how to configure content types and form modes programmatically in Drupal 8. I've created the following using the UI:


A content type named book
A form mode for content, named foo
A view mode for content, named bar


When I run drush cget, I get this list:

...
[36] core.entity_form_display.node.book.default
[37] core.entity_form_mode.node.foo
[38] core.entity_form_mode.user.register
[39] core.entity_view_display.node.book.default
[40] core.entity_view_display.node.book.teaser
[41] core.entity_view_mode.node.bar
[42] core.entity_view_mode.node.full
[43] core.entity_view_mode.node.rss
[44] core.entity_view_mode.node.search_index
[45] core.entity_view_mode.node.search_result
[46] core.entity_view_mode.node.teaser
[47] core.entity_view_mode.user.compact
[48] core.entity_view_mode.user.full
...


What is the difference between the entity_form_display configuration (36) and the entity_form_mode configurations (37, 38)?
entity_form_mode would be the form mode (/admin/structure/display-modes/form)


37 - Form mode foo available for use on node entities (shows as
content on the link above) 
38 - Form mode register available on
user entities.


entity_form_display is the configuration for that mode on a specific bundle - how the fields are arranged (/admin/structure/types/manage/book/form-display/{form_mode}) - in your case form_mode would be foo.


36 - Form display settings for the default display on the book bundle (content type) of the node entity.


The reason 36 is default is because you have arranged your form display (/admin/structure/types/manage/book/form-display) but you haven't enabled your foo mode.

At the bottom of that page is a fieldset called "Custom display settings". Expand that and you can enable your foo display for that content type.



In the picture, I have a created a form mode called Inline Entity Form, yours should say foo