@Jamval,

I am on Spectrum and have IPv6 operational.

My settings in Deco:

Hope this helps.

  @Jamval Thanks for the replies.  Initially I used the following settings:

Connection Type: Dynamic

Get IPv6 Address:  auto

Prefix Delegation: enabled

DNS Address: Auto

Assigned Type: DHCPv6

I rebooted and the Deco app is showing a valid IPv6 address, but test-ipv6.com is showing ipv6 address is not detected.

I think the problem is that I didn't give the Spectrum modem a chance to completely reboot with an internet connection established before I rebooted my Deco router. I have since read that if the router completes reboot before the modem reboot is complete it will result in a failed IPv6 test.  

So I will try rebooting again in the proper order, and if that doesn't work I will try the SLAAC+ Stateless DHCP for the Assigned Type setting.

Thanks again.

Probably want to follow @IrvSp .From experience with AT&T not necessary to reboot the gateway but there are settings on the gateway to set to enable IPv6.

@IrvSp That 2603 address is your public IP address and you probably want to mask some of it...

  @Jamval Prefix appears to be /64 2603:xxxx:xxxx:0c2d part is matching/the same...

  @jzchen 

Thanks, but like the OP, web tests all declare I do not have IPv6 capability.

Also I do not allow PING on my Router and think (I am not sure) the A/V suite would block someone?

I'll change it anyway.

  @IrvSp I have one friend and an acquaintance with Spectrum.  Neither could care less about IPv6 unless necessary...

I vaguely remember, because my BE95 is no longer the main/primary router, on the Web GUI there's a place to change the IPv6 DNS server.  (Similar to IPv4), there are several choices.

TP-Link did a good job on IPv6 introduction.

If you foul up the IPv6 settings on an ASUS router:

1.  It takes maybe an hour before your mistake takes effect.

2.  It can knock out your Internet service.

Changes in setting that require reboot automatically reboot the router, (this is valid with ASUS routers as well).

Might be AT&T specific, (as I tried with Frontier on another ASUS router and it appears to be incorrect settings and/or Frontier does not support IPv6 in our area):

Do not custom set the IPv6 DNS server address.  On that same web page almost immediately after setting an "acceptable" DNS address it should show the router gets an IPv6 address, and the Prefex number.  The DNS address, (I believe,) should be the IPv6 address of the router.  So once you set to automatic, it should send the "proper" IPv6 addresses to a Windows Machine.  At least with Windows 11, there could be 3, primary, secondary, and router IPv6 address.  (Yes I looked up the Google IPv6 DNS address, and even figured out how the :: shorthand notation works, so I input the full 128 bit address just in case there was a bug on interpreting it....

Please follow up if this helps...

  @Jamval 

@IrvSp 

I figured the first part out on my own, but just found this "Guide".  Again I have access to AT&T Fiber and remotely manage an ASUS router on Frontier Fiber....

https://community.tp-link.com/us/home/forum/topic/624176

  @jzchen 

Very limited in the Deco App on what I can set, but what I did was accept the defaults, which appeared correct. As you can tell, I've enabled Win11 to have IPv6 capability.

However, Spectrum's DNS is a "Double Stack' DNS, that means it used IPv4 first, and if doesn't 'work' or the site rejects it, it uses the IPv6 address.

I think that might be the 'cause'?

This is what Dual Stack DNS definition is:

Dual-stack DNS enables a network or device to operate using both IPv4 and IPv6 simultaneously, ensuring compatibility with both internet versions. It works by querying DNS servers for both A (IPv4) and AAAA (IPv6) records, allowing clients to prefer IPv6 while falling back to IPv4, which is crucial for modern, efficient network connectivity.

If you search for sites that are IPv6 there are many. 

I tried a few, and some don't open, other do, but they state I am using IPv4, or they just open.

It is possible the testing sites can not handle Dual Stack DNS service?

  @jzchen 

On the Deco App for the BE68 there are not a lot of choices:

The Deco during setup, made 'choices' on what it determined are needed.

Dynamic IP is correct of the choices:

So is Assigned Type:

I don't see any reason to change the 'defaults' it discovered?