@Mudslideyo 

For the Deco to obtain an IPv6 address (and a address prefix for your devices), you generally have to align the IPv6 settings of the Deco on the IPv4 settings of the Deco.

For the Deco to assign IPv6 addresses to my local devices, I choose, in the Deco IPv6 settings, to set "prefix delegation", and to set "assigned type to "SLAAC+RDNSS".

  @Mudslideyo 

What client device are you testing this on?

Windows 10/11 Ignores IPv6 RDDNS IF IPv4 is active/provided by DHCP.

Thus If the Deco is configured for SLAAC+RDDNS a Windows system will not have a IPv6 DNS server.

Note this is a (stupid) Windows decision, nothing wrong with Deco.

Note IPv4 DNS server will return IPv6 IPs as well.

If you really want Windows systems to have IPv6 DNS from the Deco, you would need to select either:

SLAAC+Stateless DHCP - But this would cause Andriods and many other devices to not get IPv6 DNS

DHCPv6 - This would cause Andriods and many other devices without DHCPv6 support to not get an IPv6 address at all.

Since Windows is generally the minorty on a network, I prefer SLAAC+RDDNS, again Windows devices can still use IPv6 and get IPv6 addresses for DNS names via IPv4 DNS servers.

  @Napsterbater 

From my tests, some devices are using SLAAC, others are using RDDNS, hence setting to SLAAC+RDDNS satisfies all devices.

As the Deco app does not show the IPv6 addresses of the devices, it is time consuming to verify if each device gets an IPv6 address.

Windows, Android, and recent printers obtain an IPv6 address.