Booting from a USB 2.0 drive was indeed successful and allowed me to fix my issue.

Thanks so much!

By the way, isn't it possible to show a boot menu, so the user can choose from different boot options?

Booting from a USB 2.0 drive was indeed successful and allowed me to fix my issue.

Thanks so much!

By the way, isn't it possible to show a boot menu, so the user can choose from different boot options?

I recently purchased a Pi CM5 laptop with an Ubuntu distro already installed on it.
I repartitioned the disk in order to install another Linux distro alongside the existing one and then proceeded with the installation.
Once successfully installed, I edited the extlinux.conf file to add a new boot section using the same kernel as Ubuntu but pointing to the new root filesystem I had just installed. I established the new section as the default one and rebooted.
The new Linux image successfully booted, but only then I realised that I had forgotten to establish the root password.
Since I had prepared a boot USB drive with the Ubuntu image obtained from this site's onedrive, in case things went wrong, I tried to boot from it.
Unfortunately I've been completely unable to boot from it or from other boot drives I have flashed (I could have sworn that I had successfully booted from that USB drive before).
So my question is: do you guys know how to boot the Pi CM5 laptop from a USB drive, so I can fix my Linux installation?
Thanks in advance.