Gateway Wifi is connected and works with existing devices but will not connect to any new devices.

My Gateway Wifi is connected and works with existing devices but will not connect to any new devices. My home wifi works really well with all the devices it is currently connected too; however, any new device I bring in to my home it will not connect with. My new tv, my Switch, etc. I have been managing, but I am about to upgrade my phone and I do not want to have the same issue with that device. I have tried chatting with Xfinity support but it ends up not understanding my issue and just restarting my Gateway - which has been really frustrating. Any suggestions? Thanks!