October - last edited October
A T3200M isn't capable of acting as a simple WAP out of the box. It's basically built as a router. It will have it's own separate network from the main router becaue DHCP can't be shut off. That means it will have the same IP address range (192.168.1.x) as the new hub, which would cause a conflict and result in the problem connecting.
If you don't mind it being a separate network, there are changes you could try. Initially it may not be a bad idea to unplug the cable to the WAN port. Then try logging in to the T3200M through a browser from a device connected to it specifically, and under Advanced look for LAN IP Settings. Change the Modem IP Address to something like 192.168.10.254 and hit the green Apply and Reboot button. Once it's done rebooting, log back in using the new IP address, go back to LAN IP Settings and set the Beginning and End IP Addresses in the boxes to 192.168.10.64 and 192.168.10.253 respectively, if they weren't updated automatically after the last reboot and still show .1.64 and .1.253. If you have to make the change yourself, hit the green Apply button at the bottom after. Once it saves the changes, reboot the T3200M again. That should hopefully clear the IP address conflict and then try conncting. You'll just have to remember the IP to access the T3200M settings is changed to 192.168.10.254 and can only be accessed by a device connected to the T3200M.
If you went to the trouble of upgrading to a WiFi6 router why wouldn't you want to use a WiFi6 WAP instead of the T3200M?