Your account here indicates Express+.
Roku Express/Express+ (prior to the new Express 4K) and Premiere/Premiere+ are lower end units with single band Wi-Fi radios that only support the 2.4 GHz band. They, and many other devices of all sorts that are 2.4 GHz only, can't even see the 5 GHz band, let alone connect to it. If you have one of these models and also a dual band router with both 2.4 and 5 GHz bands, be sure the router's 2.4 GHz band is turned on.
[Note, there have been a number of reports lately of people who have routers supplied by their Internet Provider in which the router's 2.4 GHz band was disabled by an update to the router software. They've had to have their Internet Provider re-enable the 2.4 GHz band, or in some cases swap in a new router with 2.4 GHz support.]
Within the 2.4 GHz band, Rokus use channels 1 through 11 as are used in North America. Some other parts of the world also support channels 12 & 13, but Rokus can't even see these channels. Be sure your router is set to only use channels 1 through 11. If your router supports these higher channels and also has an auto channel selection feature that may switch to one of them, make sure this is not configured.
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