I have a Samsung A51 phone. When I attempt to cast from the Youtube app the Roku Express doesn't appear (a chromecast appears from time to time so I know devices show up). I am able to use my phone as a remote and cast videos/photos that are stored on my phone so I know it recognizes my phone. I have tried numerous actions to address this:
-Confirm they are on the same wifi
-Ensure everything is update
-Gone to wifi and turned on wifidirect (the device does appear when I do this but only under wi-fi direct and doesn't when I go to youtube app)
Any ideas on why the roku express doesn't appear? I've also had a friend try to locate it under their phone and it doesn't appear as well
You didnt mention your model # or firmware version (Settings/System/About)
YouTube uses DIAL for casting to Roku devices (WiFi Direct isnt at play here, but is used as a basis for Miracast-based mirroring, though not directly in terms of the UI)
Try:
1) Disable/re-enable WiFi on your phone - try again
2) Restart all devices (Roku/phone/modem/router/gateway) - try again
3) Switch Roku and/or phone WiFi from 2.4Ghz to 5Ghz or vice versa (best accomplished with separate SSIDs for each band) - try again