Can I split my 2.x and 5.x network

Thanks, I will give it a shot!

I’ve never seen band steering break devices.  While I’m the first or one of the first to throw Att under the bus for poor wifi design, the facts are what they are.  Here’s what’s worked for me, but keep in mind I’ve moved on to using my own personal wifi system, and I suggest this to anyone wanting to avoid issues with our given gateways.  
Use the above provided instructions but instead of changing the names, simply disable the 5GHz radio temporarily until your device is connected to the network.  Once done, restore the settings and your devices should function properly to the extent the WiFi of the gateway allows.   

I had sorta the same problem. My fix was to just not use the wifi on the gateway and use my own router. I have several devices that would not work with the gateway combining or basically it was saying ill figure out whats best for you and you will like it.

Which router did you select?

I would pick a trusted name brand and ensure the product can operate in access point mode to make it easier for most to manage their home network with little to no changes to the gateway.  A general rule of thumb is the more it costs the more it can do.  WiFi 7 is out now and costs the most, but there are WiFi 5 systems out there that can still get the job done, with 6 and 6E inbetween.