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 }}"