I'm very, very happy using my new USB drive with Kubuntu 18.04 and persistent storage, but I have this challenge. I've read the documentation linked below but there isn't any "recovery mode" line on the GRUB menu.
https://wiki.ubuntu.com/RecoveryMode
How do I boot into recovery mode?
How can I start Ubuntu in Safe Mode?
Holding the Shift key doesn't display the menu. If I press the Esc key repeatedly, the GRUB 2 menu isn't displayed but the GRUB command-line appears instead, so I can't start Kubuntu into safe mode (Recovery Mode).
Also, I want to say that English isn't my mother tonge.
Thank you very much for your help. The Ubuntu Community is amazing!