Who is your ISP? People with Spectrum supplied routers seem to have to change a setting in their routers to get the app to see their Roku devices. Also, if you're using some kind of public or shared Wi-Fi or don't have control over the router you may not be able to get the app to connect to your Roku device.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.