@GiGoVX
Hello, if you want to visit the local resources, you will need to do port forwarding on the Deco first:
https://www.tp-link.com/support/faq/1797/
If you have already finished that but still cannot visit the NAS from an outside network, to locate the issue, please provide us with the below information:
1. What is the current network topology/layout? What is the WAN IP address of the Deco? If it is a public IP, there should be no issues. While if it is a private IP address, you may need to do the port forwarding for the Deco as well on the front-end modem or router.
2. If all the above has been confirmed correct, try to access the NAS from the outside via the WAN IP address: port number to confirm if it is accessible. If yes, there should no issue then.
3. As for the TP-Link DDNS, it is quite easy, you just need to register your own domain and that's it, you will then be able to visit the local resources via that domain.
I hope this helps.