If you tell me what you’re actually trying to do (play a specific game on PC? fix a real console? learn how emulation works?), I can give you a more precise, safe guide.
The retro gaming scene is a prime target for hackers. "BIOS packs" are famous for containing hidden miners, keyloggers, or ransomware. Since the average searcher expects a .bin or .rom file, they lower their guard. Xbox 360 Bios Download
The Xbox 360 does not have a “BIOS” in the way a PC does. It uses a combination of a boot ROM , a kernel (stored in NAND flash), and cryptographic keys. You can’t “download a BIOS” like you would for an old PC emulator. If you tell me what you’re actually trying