Update!!
Out of desperation I uploaded one of my previous nRF52840 sketches that uses an RTC and prints to the serial monitor. Once again, I did not touch the BOOT button, I just uploaded the sketch. And, Voila!!!, it uploaded and the LED blinked as coded and the RTC data printed to the serial monitor.
So, this knowledge leads me to conclude that the serial monitor issue I am having with the (garden_project) sketch MUST have something to do with the code.
I am elated to have made this discovery because I truly like these SEEED MCU’s. And, again, to be crystal clear - I am using the same C3 MCU RTC hookup that I posted an image of earlier. So it definitely must be the code that is causing the failed upload issue because nothing else has changed.
This is getting very interesting.
Thanks.