I use Arduino IDE for many MCUs, but am not yet familiar with the STM32 MCUS. I have the Arduino BSP “STM32 MCU by STMicroelectronics” latest version 2.12.0 plus I have the latest STM32Cube Programmer installed. If I select the upload method as STM32CubeProgrammer (DFU) and toggle the RST switch while holding the BOOT down, I see the Output window showing that it has successfully loaded my program (ASCII Table Example) at 0x800000 and also says “start operation achieved successfully”. However, after this flashing, the Serial port @ COM3 no longer shows up so the ASCII table example won’t work. I have chosen the option “USB support (CDC generic Serial” as well as U(S)ART - enabled (generic Serial). I have also tried a simple program that just toggles the D5 pin, and that doesn’t work either. At this point, I am stumped.
I solved my own problem! I was setting the board up preoperly as “Blues boards”. But, unlike other MCUs, I also had to select the board part number. The CX card uses the same MCU as Blues Cygnet board , so I switched to that (default was Swan). Now it works.