It seems that there's no way to disable the ipv6 firewall on Deco XE75 and all the incoming connections to delegated ipv6 clients in the internal network get blocked.

Adding ipv6 firewall rules does not solve the issue because the ipv6 prefix assigned by my ISP is dynamic so the ipv6 addresses in the internal network change, but the ipv6 firewall only supports simple rules based on fixed ipv6 addresses.

It is a must to have a method for disabling the Deco IPv6 firewall because in this case I have to remove the Deco XE75 and to install another router for this network since there's no way to allow incoming ipv6 connections to the internal network.

Another solution is to be able to add firewall rules based only on the subnet part of the ipv6 addresses, so that when the delegated prefix changes the ipv6 firewall rules still remain active. For an expensive router, I would expect at least to be able to disable the ipv6 firewall if it can't be configured to my needs.