old 4S to connect to Wifi, but it still says "Unable to Join the network".

I was, and yes, it wouldn't let me through. I finished the setup without wifi by connecting to itunes on my PC. The phone still won't connect to wifi, even after being network reset, factory reset, and setup as a new device (not using a saved backup). Throughout all this, still won't connect to wifi.

That person has a phone that won't update past iOS9 and can't download new apps (Duo included). And to make matters worse, they don't want a new phone either. This is the only apple device I have and will probably be the last.

I tried using my hotspot from my Android phone but the 4S wouldn't list it as an available network. I'm not sure what frequency the hotspot signal is (2.4 or 5ghz) but I'm under the impression the 4S requires a 2.4ghz signal. I have devices connected to my router which I can't disconnect.

I also don't have a USB port on my router or modem. I tried using a USB to Ethernet adapter to my router but that doesn't seem to work either.

The router was shut down completely and restarted.

MAC filtering is possible but only on devices already connected (Eero wifi5 mesh routers). The 4S never comes up on the list because it never actually completes the connection. I get notified with every new device. It has connected to this network and this router in the past but it's been so long that the device is not listed anymore in the history.

A VPN is not being used. I can't download a VPN app (after the recent factory reset to the 4S) if I can't verify my apple ID, which I can't do if I can't connect to wifi.

Everything I've done, I'm still not able to connect to any network to allow for data transfer. I've reset network settings. I've factory reset the phone itself (and re-setting it up as a "new device" rather than using a backup on file). I've factory reset it and used a backup on file in iTunes during setup. I've reached out to my router manufacturer, and they don't know why it's not working. The phone is so old that Apple would probably laugh all the way to hanging up the phone. I might just abandon my ambition of being able to utilize it for making facetime calls to a loved one that has no intention of upgrading their own phone to allow for the ability to download cross platform (apple to android/android to apple) apps such as Duo/Meet, Zoom, Skype, Telegram, Signal, Messenger, WhatsApp, etc. I guess the silver lining is that if I hand the 4S to one of my kids, they can't get to the internet, ever.

Yes. Original battery. It just won't connect to wifi. It won't get a cell signal because I don't plan on connecting it to my carrier.

I did a factory reset last night and that didn't fix the problem. That was after doing a network reset multiple times.

I have been careful to make sure the password was being entered correctly. Even checked in my network settings to make sure I had it correct.