It's possible that the Wi-Fi unit has failed in the TV, or the antenna wires have come disconnected. It's unusual, but possible. Or that where the TV is has poor signal. If you already factory reset the TV with no improvement (or at least reset the network settings) you may be stuck,
If you can give different names to the 2GHz and 5GHz SSIDs, try with different names and see if one of the two radios will work.
Otherwise, you may need to buy a "Travel Router" to plug into the wired connection and use that router to make the Wi-Fi connection. Any old router or access point than can be configured as a "wireless bridge" will do that job.
You can open the TV id you are handy and inspect the antenna wires. Assuming it uses wires - it may just use an antenna printed on the circuit board. I don't know which model Roku TV you have,
Moving to a wired connection is probably the most expedient fix.