@Chuck14
Roku devices cannot see or use 5ghz DFS wireless channels (52-140).
Under your Wireless Settings for the 5ghz band (at the router/gateway), verify that you are using either channels 36-48 (low band), or 149-161 (high band).
The Roku Express 4k+ is indeed dual-band. You can also verify if the Express 4k+ is working by connecting it to your mobile hotspot (if available) on the 5ghz band as a troubleshooting step.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102