Can't chromecast streaming services on T-mobile Home Internet

Sharing what I found to work for me. 

In my case a gen 1 chrome stick would not see the network because I changed encryption to the highest possible which is WPA3. Simply changing to 2.4ghz didn't help. The key step was to lower  the encryption level. First I changed the name and password for the 2.4ghz network and then I lowered the encryption to WPA2/WPA3 and the chrome stick now sees the network. 

i don't think you need to actually create a different network but I wanted to make sure that other devices are always connecting to the most secure side so I separated mine. My other devices connect to 5Ghz with WPA3.

Keep in mind that if you do separate the bands with different network name and password, the device you use to control those devices connecting to those networks must be using the same network.

For a laptop that won’t see the wifi network at WPA3 or WPA2 I connected with an Ethernet cable.

So it seems that for devices not seeing the newly installed network, go into the gateway GUI and change to a lower encryption.

Much of this info I also found after the fact in what seems to be a newer version of the gateway guide. Or maybe I just didn't understand the info the first time I read it because I'm not trained in this stuff. Here's the guide, see notes on page 25 about older devices: https://www.t-mobile.com/support/public-files/attachments/T-Mobile%20High-Speed%20Internet%20Gateway%20End%20User%20Guide.pdf

i hope this helps.