You're a genius, this worked :D
OK, so my phone was already in the booted Fastboot stage where the Windows method leaves you stuck.
I wasn't sure what you meant by "another fastboot.exe" but I did have another from my Mi9 folder so used that (does it matter?)
I made a copy of...
Windows error here as well. The script sure looks like it is compiling and I am running the batch with admin permission. The phone reboots... to fastboot