There are a few different Ansible facts that can be used to return information about a target systems Operating System.

• ansible_distribution can be used to return the distribution of a target system's Operating System (e.g. CentOS, Ubuntu)
• ansible_distribution_version can be used to return the version of a target system's Operating System (e.g. 9.6 if the target system is Red Hat Linux 9.6 (Plow))
• ansible_distribution_major_version can be used to return the major version of a target system's Operating System (e.g. 9 if the target system is Red Hat Linux 9.6 (Plow))
• ansible_distribution_release (this article) can be used to return a target system's Operating System Release (e.g. Red Hat Linux 9.6 (Plow))

ansible_distribution_release can be used to return the Operating System Release of a target system. Refer to run tasks on the control node if you want to run this on your control node.

For example, let's say you have the following playbook. 

---
- hosts: all
  tasks:
  - ansible.builtin.debug:
      var: ansible_distribution_release 
...

If you get the following output, the gather_facts module may be set to false. gather_facts must be set to true, or not defined at all in your playbook, as gather_facts is true by default.

TASK [debug]
fatal: [server1.example.com]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'ansible_distribution_release ' is undefined\n\nThe error appears to be in 'testing.yml': line 8, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n  tasks:\n    - debug:\n      ^ here\n"}

Running this playbook should return something like this.

TASK [debug]
ok: [server1.example.com] => {
    "msg: "Red Hat Linux 8.8 (Ootpa)"
}