Note that this is for internet. Local do not need such complicated setup.
https://kmpic.asus.com/images/2023/02/23/46690782-7392-493f-8ae4-1703bac6e665.png
on mine the first line says:
DDNS is not enable yet. You can enable it in WAN / DDNS when people need to access FTP via the domain name from WAN.
means access is only within LAN right (which is all i need)?
on the FTP share page:
mine is all OFF.