test-list.yml

# ansible-playbook test-list.yml

- name: Create sub-list
  hosts: localhost
  connection: local
  become: false
  gather_facts: false
  vars:
    input: "{{ lookup('file','list.json') | from_json }}"
    interfacelist: []

  tasks:
    - name: Create interfaces Dictionary
      ansible.builtin.set_fact:
        interfaces: "{{ input }}"

    - name: Print out interfaces
      ansible.builtin.debug:
        var: item
      when: not item.enabled and 'Gig' in item.name
      with_items: "{{ interfaces }}"

    - name: Create list with items in variable interfaces which enable is false
      ansible.builtin.set_fact:
        interfacelist: "{{ interfacelist + [item.name] }}"
      when: not item.enabled and 'Gig' in item.name
      with_items: "{{ interfaces }}"

    - name: Print out interfaces variable
      ansible.builtin.debug:
        var: interfacelist