As we’ve noted repeatedly in the Installation Guide section, Nitrux uses a custom partition layout with fixed percentages that scale with the device size or allocated space. If you don’t provide enough storage for the root partition, the installation won’t finish, as we noted in our bug tracker; this isn’t a bug in Nitrux or Calamares.
For context, on Legacy BIOS devices, Calamares may not display an error in that scenario; in that case, it is a Calamares bug (not displaying the error), since it does display an error message on EFI devices.