Hi,
I encounter a weird problem.
Until then, I had no problem compiling and flashing bluepills. Last time I did it was August of 2021 (according to backup files timestamps).
I came back to the STM32 projects after I've been working on a RasPi project from VS without any issue ; the BluePill projects don't run anymore !

Went back to the basics : Blink.
Flashed the Roger's Core (Mapple) using my ST-Link clone, compiled and flashed with Arduino IDE (1.8.15) : success.
Compiled and flashed from Visual Studio + Visual Micro : fail ! The program compiles, links, and uploads OK, but no blink ! No error message.

Settings are the same in the two IDEs :
Arduino 1.6/1.8
Generic STM32F103C6/fake STM32F103C6
upload method : STM32duino bootloader
same COM port (Mapple Mini)

Flashing using the SWD port (ST-Link), the problem remains the same. Th BluePill blinks with Arduino IDE, not with VisualMicro.

Nothing special in the logs (verbose mode).

I have about 20 *Pills, tested with half a dozen, same problem.

Visual Studio 2019 + Win10. Visual Micro is up to date, and the license is valid.
I'm used to VS : been using it since it was Visual C++ 1.0 beta/WinNT 3.1 beta march 1992 (was a MSDN subscriber at this time).

I'm really stuck !

It's probably something obvious, but I spent 8 hours on the problem, with no success...

Some thoughts ?

Stupid me !!!

The STM32 sketch in VS is written with "13" pin instead of PC13 or LED_BUILTIN !!!!!

(facepalm smiley)

And the reason why at first I couldn't get the old project to work was because of a crappy breadboard with bad contacts after 6 months.

Thanks for your quick answer and solution !!!

Problem solved. I knew it was stupid and obvious.