This gist show how remove add link in related fields in admin django. Replace field_name with your field.

admin.py

@admin.register(ModelName)
class CustomAdmin(admin.ModelAdmin):
      def formfield_for_dbfield(self, db_field, **kwargs):
        formfield = super().formfield_for_dbfield(db_field, **kwargs)
        if db_field.name == "field_name":
            formfield.widget.can_add_related = False
        return formfield