@Kevin_Z No, I have all three bands (2.4G, 5G-1, and 5G-2) configured with unique SSID names in AP mode. I am also using Guest mode with 2.4G and 5G-2 set up with their own unique names also.

So AP isolation is off, and I see now that it does have a unique LAN IPv6 IP address.

IPv6 LAN IP: FE80::B2A7:B9FF:FE3C:D9AD/64

Google devices are not the only IoT that can't be connected to this AP, I have another device, a smart socket, it also can't be connected. And yes the phone is on the same band, through the AX11000, when doing setups.

"Is the 2.4G and 5G network separated or they are the same? How about the wireless security?"

They are seperated and the security is set to WPA-PSK/WPA2-PSK / TKIP/AES, for all bands

UNRELATED:

I can't even figure out how to connect the Archer AX11000 to the Actiontec T3200 in router mode. The T3200 is a gateway modem/router, with only router LAN connection I/O. Would it have to be bridged together, and use the WAN I/O on the AX11000? Then there's the issue with the ISP allowing a second router to be connected to the internet WAN, or does bridging negate that issue. What about the MAC address of the AX, would it have to be a clone of the T3200?

Also with static IP setup for the AX11000, using a non default IP of 192.168.1.6 the AX11000 GUI web interface does not work with the default http://tplinkwifi.net URL. I can only interface using the IP address. That seems to be a GUI issue.

And another static IP address issue. With or without DHCP on or off: With my phone (for example) set internally with a static IP and within the AX11000 IP pool range and the phone connected to the AX, the AX will not "display in the connected list" the phone, even though it is connected through it, and working with the internet and the main modem/router can see it.

But lets not dwell on these potentially unrelated issues, unless you see a relationship.

Update:

Managaed to get a Google Nest Mini to connect through the AX11000 on 5G, not exactly sure what did it. But setup did NOT complete as expected by the Google Home app, though it seems to be communicating with my phone

Here's a few pieces of setup information:

1) AX11000 is in AP mode

2) AX11000 DHCP is on with a Gateway IP address (same as the T3200 main router), and a LAN IP address pool.

3) AX11000 is in AP isolation

4) AX11000 has seperated three SSIDs on 2.4G, 5G-1 and 5G-2

5) AX11000 has MU MIMO turned off on the 5G bands

6) AX11000 has LAN setting of: 

7) Host Modem/Router T3200 WiFi turned off.

  @Kamak Honestly, it's looking more and more like just plain LAN IP resolution. It was probably mostly the old Actiontec T3200 host modem/router, as I was having client IP connection issues prior to adding the AX110000. We have more than 30 connections total and more than 20 at any one time. Of those cennections approx 10 are WiFi, So I wanted to add a high bandwidth MU MIMO multi band AP to help out.

I wouldn't clasify this as resolved, just workeable at this point in time. Maybe DD-WRT will come up with a nice mod for this model. Crossed my fingers.

  @Kevin_Z I have connected some of the Google Nests to the T3200 before, but I also had to connect them to another AP we have in order for the Nests to be within range. The T3200 just doesn't have the range for out entire property.

I had tried to connect the AX11000 WAN port while in AP mode to the host router, but it could not resolve or see the internet. I was always under the impression that the WAN port could only be used for connecting to a Modem, not another router. I also tried connecting to the WAN port while in router mode, still no internet. So that might have a lot to do with the T3200 host gateway. Time to get rid of that old WiFi 5 unit. 

All aside, I have managed now, to get some IoT connected to the AX11000. I'm not 100% sure what resolved it. Was it just having issues getting IP address from the host? Maybe. I did turn off WiFi on the host router, when success occurred, but I also  had turned off MU MIMO at that time also. I've turned back on WiFi (on the host) and MU MIMO back on (on the AX) and everything is still connected, "For now"

To tell the truth, everything has issues, in my opinion and from my experience. The Google Nests, the old router, my other DD-WRT Linksys WRT32X in AP mode and now the AX11000 in AP mode, they all have issues with compatibility, I assume.

The real solution. Get rid of the old Actiontec gateway. Connect the AX11000 as a router, with the 2.5Gbs WAN straight from my ISP's Nokia ONT? Get a new TP-Link Wi-Fi 6 AX11000 AP, putting it at the opposite end of the home.