Forum Discussion
The TMobile Gateway is capable of using DFS channels and some are equipped with wifi6 (ax). Not all Roku devices can use DFS and the majority cannot use wifi6 currently. (excluding Roku Ultra 4850 and Roku-branded Plus/Pro series of RokuTVs).
Depending on the model number of your Roku device (found in Settings/System/About), may need to adjust the settings in the Gateway to get the Roku to connect again.
If you have a wifi6 TMobile Gateway, verify that you have b/g/n/ac enabled as well as ax protocols in the Wireless Settings. (ax will only be for your wifi6 devices to connect). Additionally, under your Security Settings (wifi password), verify that WPA2-Personal/PSK is enabled as well as WPA3. (WPA3 will again only be used for your wifi6 devices).
Finally, make sure your 2.4ghz band is still enabled and broadcasting on the Gateway. Give this band a separate name than your 5ghz band(s) and use a password without special characters and see if your Roku device can connect to that band.
Additionally, restarting the Gateway a few times may allow for a compatible channel to be used with your Roku device but that is kind of winging it so verifying the above settings would be better step.