> Похоже, дело именно в этом.
> Всё же непонятно, что мешает писать загрузочный раздел первым, а не пихать
> его в конец.

Я просто оставлю это здесь:
https://ventoy.net/en/doc_disk_layout.html
"About Part2
There must be an EFI System Partition with FAT filesystem and that's the mandatory requirements of UEFI specifications. So this partition is created to hold EFI boot file and other files nesscessy to Ventoy. These files are very small, so 32MB is enough. Besides, the EFI partition can be at part1 also, but I set it at part2 just because that in some version of Windows like Windows 7, only the first partition of the USB drive is visable to the system. And that's good for Ventoy's protection."