Failure installing Ubuntu 24.04 on an USB stick

[Ralf Mardorf]

PS:

This seems to explain the "unallocated" space:

"3.2 Master Boot Record (MBR) specific instructions

Usually the post-MBR gap (after the 512 byte MBR region and before the
start of the first partition) in many MBR partitioned systems is 31 KiB
when DOS compatibility cylinder alignment issues are satisfied in the
partition table. However a post-MBR gap of about 1 to 2 MiB is
recommended to provide sufficient room for embedding GRUB's core.img
(FS#24103). It is advisable to use a partitioning tool that supports 1
MiB partition alignment to obtain this space as well as to satisfy other
non-512-byte-sector issues (which are unrelated to embedding of
core.img)." -
https://wiki.archlinux.org/title/GRUB#Master_Boot_Record_(MBR)_specific_instructions