To solve another problem I am having, it has been suggested that I need to "reboot to secure (actually recovery) mode". I don't know exactly what this means.
I have been in the BIOS of my Dell XPS laptop and I have ensured that Enable Secure Boot is switched on. Does that mean that I am already securely booting?
To boot into recovery mode, follow the steps in Takkat's answer, which I also mention here.
Before the Plymouth (boot splash) screen appears, press the Shift or Esc key (could be another key, as it depends on the laptop's manufacturer) to enter the GRUB boot menu.
After you're in the GRUB menu, select Advanced options for Ubuntu.
In the advanced options, select a recovery kernel.
Wait till you get to the Recovery Menu:
In the Recovery Menu you'll find a few recovery options for your system.
resume - Boot normally to your main OS.
clean - This option cleans your OS and removes obsoleted and unnecessary packages.
dpkg - Try to fix package manager issues.
failsafeX - Start the system in Safe graphics mode.
fsck - Check errors in the file system. This option won't work in recent Ubuntu systems as the disk is mounted.
grub - Updates the GRUB boot loader (sudo update-grub).
network - Enable Wi-Fi and network services.
root - It will drop you to a root prompt to execute commands as the root user.
system-summary - Shows information about your system.
Esc is enough - it working through VirtualBox
Sep 21, 2022 at 17:04