so you manually put the board in bootloader mode with the buttons and it shows up to the PC as STM32BOOTLOADER, yes?
What driver does Devices and Printers show is being used for it ?
It should be WinUSB v6.1.7600.16385.
if it’s not, delete the driver and delete the device.
Unplug the board, and run proffie-dfu-setup.exe
Replug in the Proffieboard.
Does it show up to the PC as a Proffieboard?
If so, open Arduino, and try uploading.
If it fails, open Serial Monitor and send RebootDFU to restart the board in bootloader mode (or do the hold BOOT, press and release RESET, release BOOT button dance again), then check the driver for STM32BOOTLOADER again…
If it’s not WinUSB v6.1.7600.16385, then something on your computer is messing with the driver. Look for Guillemot stuff, or Cura3D, or Thrustmaster controller stuff (all known to screw up the STM32 driver)
Remove any/all of those things and run proffie-dfu-setup again, try uploading again, etc…