whoami.yml

---
- hosts: "{{ host_list }}"
  become_method: su
  remote_user: root
  become_user: "{{ my_user }}"

  tasks:
    - name: Who is «remote_user»
      become: no
      ansible.builtin.command:
        cmd: whoami
      register: who_is_remote_user
      changed_when: 0

    - name: Who is «become_user»
      become: true
      ansible.builtin.command:
        cmd: whoami
      register: who_is_become_user
      changed_when: 0

    - name: Who is «remote_user»?
      ansible.builtin.debug:
        msg: "I am {{ who_is_remote_user.stdout_lines | join }}"

    - name: Who is «become_user»?
      ansible.builtin.debug:
        msg: "I am {{ who_is_become_user.stdout_lines | join }}"