---
- name: Set stats test - node1
  hosts: all
  become: true
  gather_facts: false

  vars:
    bigboot_size_target: 1G

  tasks:
    - name: Test a var
      ansible.builtin.set_stats:
        data:
          __bigboot_size_target: bigboot_size_target
        per_host: false
        aggregate: false

    - name: Debug test_set_stats
      ansible.builtin.debug:
        msg: "Locally we use bigboot_size_target -> {{ bigboot_size_target }}"

...