I was unable to get the Proxmox Backup Server 4.2 ISO Installer on a USB to get past the disk selection screen to install PBS on an old Mac Mini. I am able to turn on, see the USB disks (GRUB an EFI) to select from; but it hangs after sections. I confirmed Security Settings are off. I tested the Proxmox V9 USB ISO install I created with dd on the same Linux machine that I created the PBS ISO USB on and the Proxmox install menu loaded fine. So I don't think it's my hardware. Anyone else experience this?

Does the PBS 4.2 USB work fine on other systems?

Turns out it was a bad USB. I have successfully installed Proxmox Backup Server on 2012 Mini