I uploaded and ran several sketches on an Arduino UNO compatible until recently when I thought I would also try programming a NODEMCU ESP8266. Again no problems uploading and running the sketches. And then I wanted to use the UNO again. As soon as I started Arduino IDE the appropriate serial port (/dev/cu.usbserial-1410) disappeared and could not be selected. I am using MacOS 10.15.7 so the driver is an integral part of the OS and loading one of the CH341 drivers would actually cause more problems.
I have rebooted my Mac several times and each time the usbserial-1410 reappears until I start the Arduino IDE. I have also plugged in the NODEMCU again and that works withoud problems.
I am using Arduino IDE 1.8.19 on a MacBook with MacOS 10.15.7 (Catalina).
Starting with the physical inspection is the right way to solve it... The /dev/cu... disappears because your system recognizes the NODEMCU is not present. Make sure the USB cable for the UNO is fully seated in the UNO... the USB B can feel "inserted" but not electrically connected. Your system should recognize something in a USB port if the UNO and its cable are functioning.
Thanks for your suggestion. I tested this with two other USB cables and another UNO compatible. Still no joy. After a few restarts and fiddling around with the wiring, I disconnected the two sensors and the LCD attached to the UNO - and tried again. The UNO stayed online. I rewired the sensors and LCD one at a time and tested in between and it kept working.
I can only think that in the first situation there was a problem with the wiring to the sensors and/or the LCD.
So problem solved
