“Block WAN” will block your NAS accessing the Internet, not blocking accessing your NAS via WAN. But by default accessing your NAS via WAN is already blocked.
In firmware 4.x, we have a better solution: Parental control
btw … Then I misunderstood the Access Control Blocklist:
“Access control allows or blocks access to your network from specific client devices.
A client device can’t connect to the LAN or WAN if it is blocked.”
The defination of this function changed when we add Parental control. Parental control add more flexibility so we change the original “block” function to block connecting to the router.