@paulburr52: Your Yamaha RX-V677 receiver will get a sound source signal from the TCL TV under either (or both) of the following attachments:
HDMI: Connect HDMI cable from HDMI3 port on TCL TV to the HDMI OUT port on RX-V677 receiver. On the receiver side, HDMI Control and ARC must both be set to 'On' in order for ARC to work. See pages 23 and 134 in the RX-V677 manual. On the TCL TV side, as previously stated, under Settings, System, Control other devices (CEC), Search for CEC devices, you should see your RX-V677 receiver identified with a HDMI3 identifier and an asterisk (*) signifying that it is an audio device. ARC must be enabled. In the Control other devices (CEC) menu, ARC must be enabled, but System audio control, 1-touch play, and System standby do not have to be enabled in order for ARC to work (read the TCL manual for a description of those additional features).
Optical digital: Connect optical digital cable from optical digital OUT port on TCL TV to the AV4 digital optical IN port on Yamaha RX-V677 receiver. With this method, manually switch the receiver to the AV4 input (or use the default 'TV' scene button on the receiver front panel or the remote).
With either connection method (HDMI or optical digital) , the receiver will use the default 'TV' scene setting to produce sound from the TCL TV as input source, assuming that you have not reprogrammed the 'TV' scene setting button from its AV4 input default.
While the HDMI connection using ARC will allow some additional CEC functionality (like automatically turning the receiver on or off, automatic input switching, etc.), it does not work perfectly in all cases. The optical digital connection essentially will produce the same sound from the TCL TV source (perhaps substituting Dolby Digital in place of Dolby Digital Plus or Dolby Atmos), but your ears won't hear the difference.
Both connection methods work from my TCL 55P605 to my Yamaha RX-V773 receiver. With both connected but with CEC/ARC enabled on the TV and receiver menus, ARC trumps the optical digital connection. Either way, the receiver shows the 'TV' as the receiver input source.
EDIT: Meant to say RX-V677 receiver, not RX-V667 (typo on my part).