Hi @nevj @Tech_JA @abu and all, 
after quite a while I had the opportunity to meet that friend of mine last Wednesday again.
She visited her mum and brought her laptop along.
Now she wanted me to take a look at it and hoped we could resolve the black screen problem after all.
Well, the problem presented itself last October for the first time and as a workaround she booted her Linux Lite system using the older older kernel 5.15.0.-84 ever since.
Any newer kernels would trigger the black screen problem.
After doing some more online research (using her mum“s laptop) I came up with the idea of adding the nomodeset
parameter in the line
GRUB_CMDLINE_LINUX_DEFAULT
in /etc/default/grub
. After that: sudo update-grub
.
Of course I first tried it by adding the option manually when grub appeared after switching on the laptop. The results looked promising. 
In actual fact nomodeset
seems to have done the trick.
The laptop boots perfectly even with the latest kernel (for Linux Lite), which currently is 5.15.0-101-generic.
No black screen anymore after the login procedure. 
But I noticed the desktop wallpapers were gone after that. Well, I just needed to define 4 different wallpapers for the 4 virtual desktops again. Nothing more to be done.
Everything seems to be working just fine now:
My research provided some insights as far as nomodeset
is concerned:
-
The nomodeset
parameter instructs the Linux kernel to not load video drivers during the boot process.
Normally, the kernel will attempt to initialize and use video modes provided by the hardware or configured drivers.
However, in some cases, these modes might not be compatible with the systemās hardware or may cause issues such as the black screen problem my friend experienced. By specifying nomodeset
, the kernel avoids attempting to set any specific video mode and instead leaves the display in a more basic, unaccelerated mode.
-
The black screen issue she encountered after a kernel update could be due to compatibility issues between the updated kernel and the graphics drivers or hardware on her HP laptop.
By adding nomodeset
, she effectively bypassed the automatic loading of video drivers during boot, preventing any potential conflicts or issues related to the graphics drivers. This allows the system to boot successfully and display the login screen properly, even with the problematic kernel versions.
At least that“s the hope
.
Yet I also found out this:
- Itās worth noting that while
nomodeset
can be an effective workaround for boot-related graphics issues, it may also result in reduced graphical performance or limited display resolutions, as the system will be using a basic, unaccelerated video mode.
In some cases, it might be necessary to investigate further and address the underlying cause of the compatibility issues, such as by updating or reinstalling graphics drivers, to achieve optimal performance and compatibility with newer kernel versions.
Well, for the time being I think she should use her system the way I set it up now.
If she ever experiences any (new) issues she“ll surely let me know. 
Let“s hope for the best.
Many greetings to all of you and (if you“re celebrating): Happy Easter
.
Many greetings from Rosika 