foo.yml

- name: loop test
  gather_facts: no
  hosts: localhost
  vars:
    - array_usage:
      - id: 0
        usage: 89
      - id: 1
        usage: 70
      - id: 2
        usage: 24
      - id: 3
        usage: 33
  tasks:
  - debug:
      msg: "{{ array_usage }}"
 
  - name: Set min cap
    set_fact:
      use_capacity: "{{ array_usage | map(attribute='usage') | list | min }}"

foo2

PLAY [loop test] *************************************************************************************************************************************************************************************************************************************************************************

TASK [debug] *****************************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": [
        {
            "id": 0,
            "usage": 89
        },
        {
            "id": 1,
            "usage": 70
        },
        {
            "id": 2,
            "usage": 24
        },
        {
            "id": 3,
            "usage": 33
        }
    ]
}

TASK [Set initial capacity fact] *********************************************************************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [debug] *****************************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": [
        "24"
    ]
}

PLAY RECAP *******************************************************************************************************************************************************************************************************************************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0