Two libraries that come in useful when debugging stm32duino sketches:
With Serial Wire Output (SWO) an stm32duino can write tracing and logging to a pc at high speed.
With semihosting an stm32duino can do keyboard input, screen output, and file I/O on the pc where the debugger is running.
These are just Arduino library wrappers for tools that are used in arm development.
For these libraries to work, you need a debugger probe to connect the sketch on your stm32duino to the debugger on your pc. These libraries will not work without debugger attached. Getting a debugger probe can be as simple as putting Black Magic Probe firmware on a Blue Pill. (If you prefer a commercial product instead, try a Segger JLink Edu or JLink Edu Mini.)