@jzchen:

Thank you for your reply. I was busy with other things, so I had to postpone working on this issue. I decided to start with a clean slate on the XE75, so I reset it. I decided to start with a clean slate on the XE75, so I reset it so I could check what happened at each stage. When I did so, one of the computers insisted on connecting via Ethernet to an old network, and the normal ways of making the computer forget it did not work. I finally figured it out, and will now work some more on the Deco. But I wanted to let you know that I appreciated your comments and suggestions, and will get back to you after I have had a chance to work on it some more.

Thanks, again, and I'll write as soon as I can.

  @jzchen 

Thanks for your reply. Sorry I was unable to answer earlier. Looking back, as you had guessed, I was getting confused by the temp network that the Decos created, and the NEWNetwork that I subsequently created.

To recap, I decided to start with a clean slate on the XE75, so I reset it, attached 2 desktops with a cable, and allowed it to join the temporary network. After that was done, I created NEWNetwork, and allowed the 2 PCs as well as my laptops to join it.

At this time, both desktops as well as laptops could see both OldNetwork and NewNetwork, I could join either of them. The speeds were almost 95% of what I am paying for, regardless of which network I use, and regardless of whether the Wi-Fi on the computer network was on or off. I could also see the other computers when I looked at Network in File Explorer.

I then put the Deco into AP mode, and everything came up roses, with the speeds remaining the same.

I just wanted to thank you again for your help. As I said, once I realized that there were going to be both the temporary network and then the final one, things were pretty smooth sailing.

The only problem is that even though I have connected all computers to the NEWNetwork, the desktops (which are connected to the Deco via cable), still show that they are connected to both the NEWNetwork and the OLDNetwork, and there is no option to disconnect from the OLDNetwork or forget the SSID and Password. Do you have any suggestions?

I haven’t turned off the Wi-Fi from the Verizon modem that I will continue to use. Is that why both networks are still visible, even though I did not explicitly connect to the OLDNetwork? Also, should/can I turn off the Wi-Fi on the Verizon modem, even though the 2 desktops still think they are connected to it?

Thanks

  @MollysPa No worries about not responding lightning quick!

Is it possible that the connection(s) you are seeing are:  1 connection via WiFi to the New network  SSID, and 2 Ethernet connection to the Old Network (as I believe I mentioned once you switch to AP mode the Deco becomes a wired member of the Old Network?  I believe WiFi 6E and above devices can form MLO (aka multi-link operation), meaning they can connect to two networks at the same time.  (For my son's 6E MacBook I would see it listed twice on my network, one on the wired side and also one on WiFi, same laptop but two instances).

Typically it is recommended to disable the WiFi, (in your case), the Verizon router.  This is because usually the purchased router is an upgrade and you want to take full advantage of its capabilities.  When the technician came to install our AT&T Fiber, he suggested I leave the gateway's WiFi on, sharing that he also did that in his home   He also shared that they were both using the same SSID and password (if I recall correctly).  This was a new idea to me, of course I have to respect his idea since he installs/services fiber internet for a living.  I did turn the gateway WiFi off, and to this day leave it off, because that is conventionally recommended to take full advantage of the upgraded specs of the Deco (in your case).  If you want to leave your gateway's WiFi on I guess you could change the SSID and password to match the New Network.  I still think that was a novel idea worth trying, (what the tech suggested and you currently have being both on).