Form display doesn't render field groups

Testing on a local, I am able to have field groups work on edit form, testing on the civicrm_email and civicrm_event entity types.
Using exact copy of 8.x-3.x available on D.O

In D9 you have to add a field group of type "Tabs" .. then add additional field groups of type "Tab", and nest that under the "Tabs" one, and then next your fields inside the tab groups.

if you have only a "Tabs" without "Tab" groups, or vice versa, it will not work correctly.

Using Field Group 8.x-3.4 in testing

We had a bug earlier in the year for Event and Activity types, but fixed it: I thought we took care of this here: https://github.com/eileenmcnaughton/civicrm_entity/pull/415

So field groups is supported.

My example "Entity Form Display" core.entity_form_display.civicrm_event.civicrm_event.default.yml

uuid: c60b85ee-a8cc-44d2-9eec-9e3ad441cb55
langcode: en
status: true
dependencies:
  module:
    - civicrm_entity
    - datetime
    - field_group
third_party_settings:
  field_group:
    group_fieldset_test:
      children: {  }
      label: 'Fieldset Test'
      region: hidden
      parent_name: ''
      weight: 5
      format_type: fieldset
      format_settings:
        classes: ''
        show_empty_fields: false
        id: ''
        description: ''
        required_fields: true
    group_accordian_parent_test:
      children:
        - group_accordion_one
        - group_accordion_two
      label: 'Accordian Parent Test'
      region: content
      parent_name: ''
      weight: 4
      format_type: tabs
      format_settings:
        classes: ''
        show_empty_fields: false
        id: ''
        direction: vertical
        width_breakpoint: 640
        effect: none
    group_accordion_one:
      children:
        - event_type_id
      label: 'Accordion One'
      region: content
      parent_name: group_accordian_parent_test
      weight: 21
      format_type: tab
      format_settings:
        classes: ''
        show_empty_fields: false
        id: ''
        formatter: closed
        description: ''
        required_fields: true
        effect: none
    group_accordion_two:
      children:
        - registration_start_date
        - registration_end_date
      label: 'Accordion Two'
      region: content
      parent_name: group_accordian_parent_test
      weight: 22
      format_type: tab
      format_settings:
        classes: ''
        show_empty_fields: false
        id: ''
        formatter: closed
        description: ''
        required_fields: true
id: civicrm_event.civicrm_event.default
targetEntityType: civicrm_event
bundle: civicrm_event
mode: default
content:
  description:
    type: civicrm_entity_textarea
    weight: 0
    region: content
    settings:
      rows: '5'
      placeholder: ''
    third_party_settings: {  }
    rows: 8
  event_type_id:
    type: options_select
    weight: 10
    region: content
    settings: {  }
    third_party_settings: {  }
  is_online_registration:
    type: boolean_checkbox
    weight: 2
    region: content
    settings:
      display_label: true
    third_party_settings: {  }
  registration_end_date:
    type: datetime_default
    weight: 9
    region: content
    settings: {  }
    third_party_settings: {  }
  registration_link_text:
    type: string_textfield
    weight: 3
    region: content
    settings:
      size: 60
      placeholder: ''
    third_party_settings: {  }
  registration_start_date:
    type: datetime_default
    weight: 7
    region: content
    settings: {  }
    third_party_settings: {  }
  title:
    type: string_textfield
    weight: 1
    region: content
    settings:
      size: 60
      placeholder: ''
    third_party_settings: {  }
hidden:
  allow_same_participant_emails: true
  allow_selfcancelxfer: true
  approval_req_text: true
  bcc_confirm: true
  campaign_id: true
  cc_confirm: true
  confirm_email_text: true
  confirm_footer_text: true
  confirm_from_email: true
  confirm_from_name: true
  confirm_text: true
  confirm_title: true
  created_date: true
  created_id: true
  currency: true
  custom_2: true
  custom_3: true
  custom_4: true
  custom_5: true
  custom_6: true
  custom_7: true
  dedupe_rule_group_id: true
  default_discount_fee_id: true
  default_fee_id: true
  default_role_id: true
  end_date: true
  event_full_text: true
  expiration_time: true
  fee_label: true
  financial_type_id: true
  footer_text: true
  has_waitlist: true
  initial_amount_help_text: true
  initial_amount_label: true
  intro_text: true
  is_active: true
  is_billing_required: true
  is_confirm_enabled: true
  is_email_confirm: true
  is_map: true
  is_monetary: true
  is_multiple_registrations: true
  is_partial_payment: true
  is_pay_later: true
  is_public: true
  is_share: true
  is_show_location: true
  is_template: true
  loc_block_id: true
  max_additional_participants: true
  max_participants: true
  min_initial_amount: true
  parent_event_id: true
  participant_listing_id: true
  pay_later_receipt: true
  pay_later_text: true
  payment_processor: true
  requires_approval: true
  selfcancelxfer_time: true
  slot_label_id: true
  start_date: true
  summary: true
  template_title: true
  thankyou_footer_text: true
  thankyou_text: true
  thankyou_title: true
  waitlist_text: true

Ok, thank you. I've got a good setup, so maybe it's something altering/disabling it. No errors in DevTools.
I'll have a look, debug and let you know the result.