Bootloader update process:
1. Install OS-V3.09 or a newer version on the cartridge.
2. Download bootrom-v5.xx.b64.
3. Run the cartridge on an original N64 console (it will not start on Analogue 3D with an older bootloader).
4. In the cartridge menu, select the bootrom-v5.xx.b64 file and start the installation process.