Dell laptop won’t recognize home Wi-Fi

Are you using an Xfinity rental gateway?   Hard to guess what you are using.  What model number?

Their new one uses combined 2.4/5Ghz signal band steering.  Their version doesn't work with a lot of radio chipsets.  That may be the case with your dell.  It's also possible your gateway's WiFi radio is dying if it did work, and now it does not.  Swap it out.  It's a rental.  The fast way is doing that at an Xfinity store.  Does anything else connect to it?   

You may be able to select WiFi "modes" as Xfinity calls them with the phone app, or you won't have the option depending on the firmware it is running.  That may have been updated 4 weeks ago.  More information:

https://www.xfinity.com/support/articles/change-wifi-channel-xfinity-xfi 

https://www.xfinity.com/support/articles/benefits-same-wifi-network-password-name-xfi-gateway 

You might be able to a get your laptop to work by using a small 802.11ac usb WiFi adapter on your dell.  They're around $10-15 on Amazon.  You may be able to update the internal radio in your laptop to a radio that can speak WiFi 6 -- that is very much laptop model specific, and if anyone makes one for it that will fit and can plug into the same slot on the motherboard. 

You could get a cheap 802.11 b/g/n WiFi access point and connect to that instead.  That would help other devices that can't connect to your gateway's radio.  You could also use a 3rd party gateway that can speak the same WiFi standard as your dell, and not have the problem.  Look up the service tag on the sticker on it at the dell site to find out what you have for WiFi hardware, and the WiFi standards it speaks, as well as your other gear before buying a gateway or mesh network system that is compatible.