When installing Nitrux on a computer with multiple storage devices and selecting an MBR disk as the installation target, Calamares may not select the same device, causing an error during GRUB installation. This issue was very common with Legacy BIOS computers.
As mentioned, we strongly discourage using MBR storage devices. Users who choose to continue the installation despite our recommendations must ensure that the disk with the MBR partition table is the same disk on which Calamares will install Nitrux. Otherwise, Calamares will fail to install GRUB. This discrepancy in target device selection is a Calamares bug, since it is not configurable.
However, most importantly, Nitrux does not support Legacy BIOS hardware; Nitrux supports only UEFI systems.