If you have soldering skills and a BIOS programmer (like a Raspberry Pi Pico or TL866):
Most up-to-date Xemu guides recommend the 512KB MCPX ROM because it better emulates the hardware behavior of the most common retail consoles. Mcpx Boot Rom File For Xemu
Once verified, it transfers control to the BIOS (Flash ROM) to finish the boot process. File Details for xemu: If you have soldering skills and a BIOS