Hello @Handian Sudianto ,
Welcome to Microsoft QnA.
Could you please post the link url of "Add a public IP address to the VM's network interface".
Have you configured any public IP address on your VM, or the VM's are strictly being operated via private IP?
There isn't anything to worry about. The default suggestions are Azure Platform suggestions specific to RDP so that customers don't have to face generic RDP issues.
Since you do not require a public IP address, so it is absolutely fine, because you have configured a private IP address already.
Hope that resolves your doubt. If you have any further questions, do let me know in your comments below. Thanks ! :)