I've installed Ubuntu on a USB drive using another Ubuntu Live USB.
I've formatted that drive with a single partition and mount point
The Live USB then fully installed Ubuntu there, and it finished successfully.
However, I can't seem to be able to boot Ubuntu from that drive.
The Live USB was created using Rufus and was configured to use GPT and boot in UEFI mode, which it does. I also don't have Secure Boot enabled in my UEFI configuration.
What could be the issue that prevents the installed Ubuntu drive to boot? Could it be installed with MBR for BIOS? How do I prevent that during the installation?
If I try to boot in CSM mode, grub shows up in rescue mode.
I've never had an issue booting the Live USB drive.