Thank you for your help!
In fact, this was also my first guess, and what I tried first. But I was not sure about the error I got.
Now I will take a closer look and download or install the missing part:
Arduino: 1.8.12 (Windows 10), Board: "Generic STM32F1 series, Generic F103VE, STM32CubeProgrammer (SWD), Enabled (generic 'Serial'), None, Low/Full Speed, Smallest (-Os default), Newlib Nano (default)"
WARNING: library GxEPD_HD-master claims to run on STM32, STM32F1, esp32, esp8266 architecture(s) and may be incompatible with your current board which runs on stm32 architecture(s).
Sketch uses 509612 bytes (97%) of program storage space. Maximum is 524288 bytes.
Global variables use 50708 bytes (77%) of dynamic memory, leaving 14828 bytes for local variables. Maximum is 65536 bytes.
Low memory available, stability problems may occur.
STM32_Programmer_CLI.exe not found.
Please install it or add <STM32CubeProgrammer path>\bin' to your PATH environment:
An error occurred while uploading the sketch
This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.