Modular pages: blueprint does not get picked

Hey community,

I don’t really seem to grasp the how to of modular pages. I have \blueprints\modular and emplates\modular folders. And in the admin the template gets selected. But my modular\modul_soundesign.yamlfile does not get picked.

Before the page was not modular and had lost of sections that repeated. I thought making it modular would give me the chance to not repeat myself and extend one blueprint.

My Blueprint for the modular page:

title: Produktion
'@extends':
    type: standard
    context: blueprints://pages

form:
  fields:
    tabs:
      type: tabs
      active: 1

      fields:
 
# in the extended blueprint is one tab before and one after the "Inhalt Tab"
# Inhalt Tab
        content:
          items: '@self.modular'
          # order:
          #     by: default
          #     dir: asc
          #     custom:
          #         - _sounddesign
          fields:
            content:
              unset@: true
            uploads:
              unset@: true

# -------------------------  ANSPRECHPARTNER

            ansprechpartner_section:
                type: section
                title: Ansprechpartner

                fields:
                  header.ansprechpartner_title:
                    type: text
                    # size: large
                    label: Anprechpartner Überschrift
                    placeholder: 'Fragen? Rufen Sie mich an!'
                    style: vertical

                  header.ansprechpartner_text:
                    type: editor
                    label: Text

And for the modul:

title: Modul Sounddesign

form:
  fields:
    tabs:
      type: tabs
      active: 1

      fields:

# Inhalt Tab
        content:
          fields:
            content:
              # toggleable: true
              label: Standard Content Editor
              unset@: true
            uploads:
              unset@: true

# --- Kategorie
            sektion:
              type: section
              title: Leistung / kategorie
              # text: Mhm was schreibe ich hier drunter...
              fields:
                header.leistung.title:
                  type: text
                  label: Leistung / Kategorie - Titel bzw. Überschrift
                  style: vertical
                  placeholder: 'Sounddesign'
                  default: 'Sounddesign'
                header.leistung.text:
                  type: textarea
                  label: Text
                  style: vertical
                  placeholder: 'Die Welt, in der wir leben, ist voller Töne, Klänge, Geräusche...'
                header.leistung.referenzliste:
                  name: Referenzliste
                  type: list
                  style: vertical
                  collapsed: true
                  label: Referenzen
                  btnLabel: Neue Referenz Hinzufügen
                  fields:
                    .title:
                      type: text
                      label: Titel / Überschrift
                      placeholder: 'Referenz Titel'

                    # and lots of more fields coming
----

Nevermind. I tend to over improve and forget about my deadlines. Also the client started working with the page already… So I should better keep on track.
Will go back to a non modular page and dig into this deeper next time.