The have been several posts asking how to fix the following warning, without a clear answer (IMO).
[DEPRECATION WARNING]: DEFAULT_SUDO_USER option, In favor of Ansible Become, which is a generic framework. See become_user. , use become instead. This feature will be removed in version 2.8. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.
You need to edit the ansible.cfg file
$ sudo vim /etc/ansible/ansible.cfg
Comment out the "sudo_user" option set in the "[defaults]" section.
#sudo_user = root
remove the comment from all lines in the "[privilege_escalation]" section
You should no long get the deprecation warning when you run ansible commands.