Dear Tom, thank you, I appreciate your help very much.
I went through all the steps.
After the reboot, the display and peripherals works. But only until the next shut down / restart. Than, there is 0x56 address again and the display is not working.
So, I am able to keep the display working only after the fresh STM32 flash, till the next power off/power on. I really don’t know, what is bad, I adhered all the points on seed’s wiki and also in your guide.
I also reflashed the rpi image from seed again.
Should I perform repeated flash through openOCD? I performed it yesterday repeatedly, but with the same result.