My advice?
Continue booting using Advanced Options for Ubuntu and selecting the Linux 6.8.0-49 kernel.
I would also update/upgrade using the terminal and not Software Updater as that utility will install a kernel and remove an older kernel at the same time.
You could be in a situation where a newer kernel is brought in that is also broken in some way and the one working kernel (Linux 6.8.0-49 is automatically removed.
Wait until you get two newer kernels that work before you use Software Updater again or run autoremove.
This is what I have done in the past. In fact, earlier on in the year I had an install of Ubuntu 20.04 LTS that was so broken it could not be used. I was on the point of installing over it when I decided to give that install one more try.
I used advanced options recovery mode. At the recovery menu I selected Network to establish an internet connection. Followed by Root shell prompt and I ran apt update and apt upgrade. close to 500 packages were downloaded and installed.
A reboot gave me back a working Ubuntu 20.04 LTS.
Regards