You are using the Maple core which is incompatible with this library. You should use the bluepill_f103c8 board target which uses the STM32Duino core.
I have personally built up a Bluepill + W5500 module setup and implemented two projects:
- Ethernet webserver via Ethernet library: GitHub - maxgerhardt/pio-bluepill-w5500-ethernet-webserver: A simple example demonstrating using PlatformIO with a Bluepill and Wiznet W5500 board.
- MQTT client via mqtt-arduino and Ethernet library: GitHub - maxgerhardt/pio-bluepill-w5500-ethernet-mqtt-client: An example project with a Bluepill and W5500 board implementing an MQTT publish-and-subscribe client.
Both projects are working perfectly fine with the provided platformio.ini and no changes to the library have been made.
