@csaltos In short, you can disable the warning message by explicitly turning off security, i.e. add the following in elasticsearch.yml:
xpack.security.enabled: false
Some more context
The warning is shown when the security is implicitly disabled, that is, there is no config for xpack.security.enabled in elasticsearch.yml, and your license is either basic or trial. This is new in 7.13. You can remove the warning by either enable or disable security explicitly. We'd recommend you to enable security since it gives you better protection. But in the meantime, you can choose to opt out explicilty. Again, we recommend enabling security since your data could be at risk without it. The new step-by-step guide should provide you a straightforward path. Thanks!