The thing about flash drive age and quality is just BS. I tried to boot of a virtually created USB-flash backed by NVME-drive. Same issue. Had to create the disk 3 times and it just worked. This was on an IBM NVME SAN Volume that runs hundreds of VM's in ESXi. I would say there is something fishy with unraid install maker. I had the same thing happening on my Macbook pro M4 pro.