Why won't Ventoy boot a Microsoft Windows 10 ISO file?

[Renatus]

Sorry, not very clear...
The standard Ventoy drive has NOTHING on partition 0 - so how can you boot from it?
https://ventoy.net/en/doc_disk_layout.html
Both the legacy and UEFI boot files are on partition 1 (2nd partition)
The Ventoy menu displays the mode it has booted in and normally the BIOS also gives you a clue too, e.g. EFI: USB Kingston (Partition 1).
The BIOS menu often numbers partitions starting from 1 though (not 0) - so don't be confused by that.

So are you saying that if you place two Windows 10 x64 ISOs onto the first partition, then UEFI64 boot to Ventoy, you can boot to the older ISO but not the newer one using the same BIOS settings? 
P.S. Presumably you have formatted the first large partition as something which Windows can read (e.g. NTFS)?

In the NUC, Partition 0 corresponds to Partition 1 on the scheme and NUC Partition 1 to scheme Partition 2, and of course it can boot from NUC Partition 0 (or 1 on the scheme) because it's a legacy boot, so it boots from the MBR, doesn't need EFI partition for booting.
I did not reformat any partition, I just used the Ventoy tool, so the first partition remained with the original format (ExFAT).
Answering your question: "So are you saying that if you place two Windows 10 x64 ISOs onto the first partition, then UEFI64 boot to Ventoy, you can boot to the older ISO but not the newer one using the same BIOS settings? ", yes precisely that!
Just wanted to add I am an IT specialist, so I know very well what I am saying, and I am not a bit confused.