Hi what version  are seabios is use by Unraid 6.9.2 ?   Perhaps  it just me there google  it badly but can't  find it

I think you can see the version during boot:

Example image:

 

 

If you need latest/custom/ specific version of seabios, just compile it and set the vm xml to point to the compiled bios:

  <os>
    ...
    <loader>/path/to/compiled/seabios/bios.bin</loader>
    ...
  </os>