Ansible – Print message – debug: msg=”line1 \n {{ var2 }} \n line3 with var3 = {{ var3 }}”

debug module support array, so you can do like this:

debug:
  msg:
    - "First line"
    - "Second line"

The output:

ok: [node1] => {
    "msg": [
        "First line",
        "Second line"
    ]
}

Or you can use the method from this answer:

In YAML, how do I break a string over multiple lines?