playbook.yml

    - debug: msg="{{ ec2 }}"

    # Since you're looping over ec2 creating instances, instead of ec2.tagged_instances or ec2.instances you'll need
    # to iterate over the results list created due to with_items
    
    # Brand new instance can be accessed with either the instance_ids list, or instances list
    - set_fact:
        only_new_instances: "{{ ec2.results | json_query('[*].instance_ids') }}"

    # New and old hosts that match the count tag are always in the tagged_instances list
    - set_fact:
        instances_matching_count_tag: "{{ ec2.results | json_query('[*].tagged_instances[*].id') }}"

    - name: Create and associate EIP
      ec2_eip:
        in_vpc: yes
        reuse_existing_ip_allowed: yes
        state: present
        region: "{{ region }}"
        instance_id: "{{ item }}"
      register: elastic_ip
      loop: "{{ instances_matching_count_tag }}"