Hi,
Summary
being stuck in shell instead of booting happened to me quite regularly after OS updates, most recently when updating to 11.5.
Before I managed to overcome this by creating a new VM with the same parameteres, which would probably work again. I’m using Windows VirtualBox VM.
This time I wanted to learn a quicker workaround, so I profited from the info here and other related threads.
In my bios I could not find the option to disable the secure boot.
However, changning the boot order in the bios helped immediatley and keeps on working after further restarts - there used to be the CD-ROM of the VM at the first place, so I put the HDD option to the top instead of the CD-ROM.
Summary
Sorry for not posting printscreens, at this moment I do not know how to get back to the bios to document my proceeding.
Thank you all for sharing your experience here, it helped me!