T-Mobile won't connect to Roku TV

I doubt that you would find an Arcadyan or Sagemcon gateway on DFS channels. Their configuration is so limited it is probably not an option. The Nokia is another story as it does support the configuration of those 5GHz channels. I could be mistaken but I don't believe the Arcadyan or Sagemcon have as extensive configuration for wifi channels.

Since there are so many different Roku models I would just guess it is either an older one without 802.11ac or ax or the authentication type it requires might not be available. If the gateway is defaulting to WPA2/WPA3 and the Roku model requires WPA then the authentication type on the gateway needs to be configured to allow the needed authentication type. Not having WPA authentication type available is one of the most common issues when connecting earlier generation wireless adapters.