This issue has been solved.  Here's what I missed:

Under the TOOLS menu, there is a selection titled "USB CDC On Boot "Disabled"   

It needs to be ENABLED.

Apparently, that is disabled by default, as I do not recall every changing it.

  I would guess (with only flimsy evidence), that this problem might apply to any ESP32-C6 (and probably ESP32-C3) based board, rather than just limited to BEVRlink products, so widening the possible search for an answer.

On this hypothesis, a bit more Googling suggested that ESP32-Cx devices have exhibited reluctance to make Serial comms work, apparently due to a more complex UART arrangement, compared to the earlier ESP32. I haven't tracked down a full explanation, but honourable mentions include:

https://espressif-docs.readthedocs-hosted.com/projects/arduino-esp32/en/latest/guides/tools_menu.html

section:     USB CDC On Boot

 and questions on Arduino forum, such as:

https://forum.arduino.cc/t/esp32-c3-and-serial-monitor-arduino-ide/1198965

and

https://forum.arduino.cc/t/unable-to-get-data-on-serial-monitor-from-waveshare-esp32-c6-zero-module/1297769/3

also discuss the issue.

I haven't looked into it properly, so I am rather confused as to the 'correct' answer, (and I don't have any hardware to test it on), but first impressions suggest that the Arduino IDE may require an option under Tools to be set, and the Espressif doc mentions Serial0, instead of Serial.

Perhaps you can find some more information, and try out any hopeful suggestions.

Good luck and best wishes, Dave

--------------------

PS .. Although the reply from @mic70252 appears above, it wasn't visible when I started this search. So maybe my comments below are now 'Out of Date' ... apologies for any confusion.

I just tried the link from @mic70252, and with Firefox, I still get the "Unavailable in this country" page, instead of useful information.

However, I just tried with Chrome, and I finally get a more useful looking page. 

I am beginning to wonder how many more obstacles I can find, just to figure out what this product is. I hope using it, proves easier to anyone buying it. 😉 

-------------------

  Courtesy of Google, I recorded my search findings ... hopefully there will be something useful in the diatribe for someone ... though not for me, as explained at the end. 🤔 🤔 🤔

------------------

   Amazon advert mentions it: //www.amazon.com/BEVRLink-Channel-Relay-HAT-Raspberry/dp/B07Y7NY42C

(Please copy and paste link to your browser.)

4 Channel Relay HAT for Raspberry Pi 5 - Also Works with Raspberry Pi 4B and Raspberry Pi 3 (Raspberry Pi Board is NOT Included)

You can add more relays using BEVRLink standard relays (5V, 12V, or 24V) along with its PSU. These standard relays will power both the 4-channel relay and the Raspberry Pi, eliminating the need to supply power to the Raspberry Pi via USB-C. They will also provide power to any additional relays connected after the BEVRLink standard relay

and the comment:

Access to documentation simply by scanning the QR code on the packaging.

------------

and there is a BEVRlink 'store' on Amazon, listing several variants on this theme:

//www.amazon.com/s?me=AIHF7LBXLT1TR&marketplaceID=ATVPDKIKX0DER

And manualsplus at https://manuals.plus/category/bevrlink   offer the single (unhelpful) sentence

"Discover the versatile 4 Channel 12V WiFi Relay Module, Model BEVRLink, with ESP32 C6 microcontroller. Explore its specifications, installation instructions, pinout details, and FCC compliance requirements in the comprehensive user manual and safety datasheet."

-------

Also, courtesy of Google + Reddit (https://www.reddit.com/r/FCCID/comments/1flvygv/gothenburg_design_ab_bevrlink_4_channel_esp32/), it seems an FCC application was made, but I can't find any way of accessing useful information, like the schematic, which was apparently included in the application.

https://fcc.report/FCC-ID/2BKZL-7350001161815

------------------------

This Amazon page looked more promising:

//www.amazon.com/BEVRLink-Module-Channel-Bluetooth-Zigbee/dp/B07Y7NYWHF?m=AIHF7LBXLT1TR&marketplaceID=ATVPDKIKX0DER

Including a link to user manual:

//m.media-amazon.com/images/I/B1aqIekX8KL.phttps://bevrlink.com/products/bevrlink-4-channel-esp-relay-module-12vdf

Which in turn has a QR code and another link

https://bevrlink.com/products/bevrlink-4-channel-esp-relay-module-12v

I haven't tried the QR code, but the link came up with a page saying :

Apparently, the UK is not regarded as a 'friendly' country. Maybe, others will have more luck.

---------------

Best wishes, Dave

https://bevrlink.com/blogs/control-options/getting-started-with-bevrlink-relay-4-4-buttons-esp32-arduino

The example code shown on the above web page (Step 7: Controlling the Relays Over Wi-Fi) does not make any unusual references to the Serial UART.

I am also looking at the through holes (J7) where I see RX, TX, GND as another place to tap if I cannot figure out how to get the standard USB port to display console output.

Thank you.

Can you provide a link to this product's documentation? It would be easier to assist you with some more information.

😎

Bill

void setup() {
  Serial.begin(115200);
  delay(2000);
  // Give time for initialization
  Serial.println("Hello from ESP32-C6!");
}

void loop() {
  // Do nothing
}