Arduino for STM32

In my day job I am a professional software developer (Java). And in my free time I code for Arduino community. I develop Arduino libraries and contribute to existing libraries and cores. Most of my libraries or libraries I maintain are architecture independent so should work with stm32duino boards too, but I focus on AVR, SAMD, ESP and a little nRF5. I have the Blue Pill board, but unfortunately I rarely test my libraries with it. Now when the STM32 community has this forum again, I will seize the opportunity to ask for help with some problems I have with the Blue Pill.

my GitHub repository with Arduino libraries https://github.com/jandrassy
some of the libraries are in Library Manager index

welcome @Juraj

Nice to see you there.
Hope we will be able to help.

I tested my WiFiEspAT and StreamLib with Blue Pill with STM32 and with STM32duino boards packages. Both work.
Some small adjustments were necessary for Roger Clark's core in WiFiEspAT library (some fake _P functions and include itoa.h, because it is not in Arduino.h ).
And I retested the UIPEthernet library (2.x), which I maintain a little.

I had strange problems with loosing USB port (and bootloader) on USB connector so I left the ST-Link connected to board. I turned out it was the cause of the problems . I had enc28j60 module and SD card connected and with STLink disconnected from USB and powered over the Blue Pill I run into brown out.