I had my Roku soundbar setup and with my Vizio SmarTV via HDMI to the ARC HDMI port and everything was working fine then I had to unplug the TV power because it wasn't responding when trying to turn it on. Since then I get no TV sound out of Roku (sound from Roku streaming works fine). I just did a factory reset of the TV but same thing.
When I check the CEC settings in the TV it's enabled. I had it do a search for devices and it said no CEC devices found. I swapped HDMI cables but same thing. I've checked Roku for a software update but it's already up to date.
Did the ARC port on the TV go bad? Is there a problem with Roku? With 2 HDMI cables? (This one seems unlikely)
1) You didnt mention your Roku's firmware version: Settings/System/About ("up to date" is meaningless because Roku uses model-specific releases and staggered rollouts)
2) Turn off and Unplug your Roku soundbar and your TV from AC power for 5-10 minutes.
3) Then plug in and fully power up the soundbar (give it a few minutes).
5) Plug in and fully power on the TV.
4) Search for devices/Check sound (verify the Vizio is configured for HT/external audio)