Plone 6 classic custom add/edit form

Development Developing for Plone
2

This does the job in plone6 for me:

<!-- collection.xml in profile/default/types-->

<!--
Name of add_view_expression must be match with the Name of the Adapter 
-->

<!-- View information -->
<property name="add_view_expr">string:${folder_url}/++add++Collection</property>

<!-- configure.zcml -->
<!-- Register custom AddForm for Collection Type -->
  <adapter
    for="Products.CMFCore.interfaces.IFolderish
      zope.publisher.interfaces.browser.IDefaultBrowserLayer
      plone.dexterity.interfaces.IDexterityFTI"
    name="Collection"
    provides="zope.publisher.interfaces.browser.IBrowserPage"
    factory=".views.CollectionAddFormView" />

# yourformviews.py
from plone.dexterity.browser.add import DefaultAddView
from plone.dexterity.browser.add import DefaultAddForm

class CollectionAddFormView(DefaultAddView):

    form = CollectionAddForm

    index = ViewPageTemplateFile("templates/collection_add_edit_form.pt")

class CollectionAddForm(DefaultAddForm):

    portal_type = "Collection"

   def updateFields(self):
        super(CollectionAddForm, self).updateFields()

   def update(self):
        super(CollectionAddForm, self).update()