Usually this is not needed and poses the risk that you accidentally kill the bootloader. If anything, only flash the bootloader and carefully stick to the instructions: FYSETC-SPIDER/bootloader at main · FYSETC/FYSETC-SPIDER · GitHub
From the symptoms either:
- potentially a killed bootloader
- board not correctly flashed
- not correctly connected
Carefully follow the pointers given in Issues flashing the printer board