This is the bootloader only. You need to have an application installed (Klipper, Marlin, etc) in addition to the bootloader for the device to be recognized
You'll need to be able to connect to the board via UART or with an ST-Link (latter preferred)
- Flash the bootloader starting at address 0x08000000
- Application flash at 0x08000800
I used an ST-Link + STM32CubeProg to flash the bootloader.
Flash Loader Demonstrator is also a solid tool if you are connecting via UART
There are a billion ways to flash firmware+application to your device. Klipper's docs are a good resource for this
I have included the bootloader only file as well as a bootloader with Klipper preinstalled. You'll want to update or reinstall klipper after install
Before committing yourself to this - make sure you have the time, patience, and tools to fix it if you break the bootloader. I'm not liable for you killing your board if you do!
Lastly - when compiling klipper firmware going forward - bootloader offset should be set to 2KiB.