I have the same issues that everyone else has mentioned on this thread but the solutions proposed don’t seem to work for me. I have changed the wireless channel to 157. I have changed the SSID for the 5G connection. I’m not sure what else to do do my Roku can find it. But it’s putting a downer on my viewing experience.
If 5Ghz is working on other devices and you are sure your model has a wireless adapter that supports 5Ghz - you should contact Roku and see if they have any advice.