#if defined(__STM32F1__) || defined(ARDUINO_ARCH_STM32F1) // Recommended original Arduino_STM32 by Roger Clark.
# if !defined(strncpy_P)
// this define is not included in the pgmspace.h file :-(
#define strncpy_P(dest, src, size) strncpy((dest), (src), (size))
# endif
#endif
Is there any reason, that the definition of strncpy_P is missing in your pgmspace.h?
For example here and here is is included.
So I must include
in my library to make it compile 😞