Roku models Express, Express+, Premiere, and Premiere+ cannot connect to the 5 GHz wifi band, only to the 2.4 GHz band. If you have one of these models and a dual band router with both 2.4 and 5 GHz bands, be sure the router's 2.4 GHz band is turned on.
Also, there have been a number of reports lately of people who have routers supplied by their Internet Provider (mainly Spectrum) having their router's 2.4 GHz band disabled by an update to the router software. They've had to have their Internet Provider re-enable the 2.4 GHz band and make sure it is set to 20 MHz bandwidth, or in some cases swap in a new router.
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