Are you sure that your player or TV has the ability to utilize the 5Ghz band? Not all can. If it can, you should be able to connect in the same manner as the 2.4Ghz band.
Are you able to connect any other devices to the 5Ghz band?
Might you have disabled the 5Ghz band in the modem? Preferably with a LAN cable connected device, do you see any State Code other than 0.0.0 in the System Summary box on this page?
I'm not a 'professor" but I believe it's because Roku is not 5G compatible therefore only recognizes the 2G signal. Had the same issue with a printer and that's the explanation I found in a FAQ.
added: noticed another response was made while I was typing.
I see it's your first post here, so welcome to the community! GabeU and tmiller1958 are on the right track. If a device can't recognize a 5 GHz band network, you might want to check if the 5 GHz network is enabled, and that the device is dual band and can use 5 GHz. I checked out the Roku website and only 3 current Roku models are dual band:
Roku® Streaming Stick® 3800R
Roku® Streaming Stick®+ 3810R
Roku Ultra 4661R