This article shows how to block your LAN users to get access to  certain countries web servers.

Please note this application note applies to current model routers (as of March 2022) such as the Vigor2927 series.

See also this FAQ:

The internet landscape sees a constant influx of new WAN IP addresses, each being allocated to novel country locations. This ongoing expansion significantly complicates the task of maintaining up-to-date records so do not be surprised if you discover that some new IP addresses have been omitted. DrayTek try to regularly update the country codes in the firmware but it may not always be completely up to date.

Note also that many hackers use a VPN to hide their true IP addresses, which makes this feature less useful for WAN to LAN traffic, but still a great tool if you want to block LAN users from accessing certain countries.