Ultra LT, model 4801, detects 2.4ghz wifi but not 5ghz. There is an older post about bandwidth compatibility but I am not familiar with how to change these settings and some internet searches advise not to. Any suggestions would be appreciated.
Roku devices don't support all 5GHz channels. You can look up DFS channels (that aren't supported), but basically you need to use a channel below 50 or above 150.
@jackcmcd- Another thing to consider.
If your router does have both 2.4 and 5 GHz wifi bands but uses the same network name (SSID) for both, as some are configured to do, you may not be able to control which band your Roku will connect to. If you can go into your router's setup and assign different SSIDs to the 2.4 and 5 GHz bands, then your Roku should find and list both, letting you select which one to connect to.
Edited to add:
If you can tell us the make and model of your router, someone here will probably be able to how you how to configure it.