from the first glance it seems that it has something with no_create and no_create_edit options
you can apply this on a m2o field and try to see the different cases possible
<field name="course_id" options="{'no_create': False, 'no_create_edit':False}" can_create="True" can_write="True" />
in brief:
can_write: allow the edition of related records (default: true)
can_create: allow the creation of related records (take precedence over no_create option),Same as can_write but adds an extra global setting for anonymous access (ANONYMOUS_CREATE)
https://www.odoo.com/documentation/13.0/reference/javascript_reference.html#relational-fields
gd luck!!!