Once in a while, I get a BLSOD on Kubuntu 22.04 and perhaps the previous versions as well.
This happens when there is a kernel update or a nvidia driver update.
I use nVidia’s drivers, since I have a GTX 650.
It doesn’t happen each time. This problem happens rarely.

***************SOLUTION:
This time, I solved it by downloading nVidia’s driver from their website.

Boot up Kubuntu, you get the splash screen and eventually the BLSOD.
Press Ctrl-Alt-F2. This gets you to a virtual console.
Log in with your account.
You would need a working PC to download the nVidia driver, copy to a USB stick.
Put the USB stick in the broken PC and you would need to mount it and copy the file to your home drive.
Set the Execute flag.

Run the nVidia driver installer with:
sudo ./NVIDIA.....whatever the file name is
and follow the instructions.
No, you don’t need to install 32 bit support.
It will complain about some path not being found, something about egl......
We don’t care about egl. Games don’t use egl or GLES. That’s for games on cellbones.

You would also need gcc and make
sudo apt install gcc
sudo apt install make

since the nVidia installer needs them.

During the install process, it will stay at 99% for a long time, depending on your CPU speed.
Once finished, it returns you to the command prompt.
Type
shutdown -r 0
and it will reboot immediately and everything will be fine.

I don’t know if you would have to update the nVidia driver manually in the future.