I think I got the concept of how to jump to the MCU built-in bootloader but I never got it working. And often information is opposing each other.
My requirement is simple and very common, hence I hope somebody has code at hand. I am fed up with trying and trying.
I have a USB CDC connection, and enter commands there. One command should be "boot to MCU bootloader" which would disconnect the USB and make the MCU appear in the DfuSeDemo tool. As if I manually disconnected the the board, pressed the Boot0 button and power it while button pressed.
Source Code can be found here: GitHub - wernerdaehn/CC3D-CableCam-Controller: CC3D and STM Cube based CableCam controller
Nothing special, standard memory layout etc.