Not exactly the same issue in my case, but for some reason I can’t control screen brightness after upgrading to kernel 7.0.0-28 in my Lenovo ThinkPad X250 (Intel HD Graphics). The brightness control popup appears in KDE but it has no effect.
If I downgrade to kernel 7.0.0-27 I can control brightness just like normal, so there’s some regression in the latest Ubuntu kernel.
Moved to a new topic.
“Not exactly the same issue” seems like you have a different problem, so let’s not confuse everybody by trying to discuss two different problems at the same time.
If you believe that you have discovered a kernel regression or bug, please file a bug report.
Have you tried the boot option
acpi_backlight=native
Four “Me Too” Posts deleted.
Folks, a quick reminder of some Ubuntu Discourse etiquette:
Please use the 
icon instead of “Me Too” posts that merely add noise to a topic.
Ubuntu Discourse is the wrong place to report a bug.
Your fellow users here can help you to determine of your problem is a bug or not, and can advise you how to report a real bug. But they won’t report it for you.
Ubuntu Discourse is not the bug tracker.
Discussion about diagnosing and triaging bugs, and about patches and fix releases, should all take place on the bug tracker.
After adding that parameter the backlight is turned up to maximum brightness, brightness controls appear in KDE but they don’t have an effect. This is running Ubuntu’s 7.0.0-28 kernel version.
I do get this messages when running the command sudo dmesg | grep acpi:
[ 5.192706] thinkpad_acpi: This ThinkPad has standard ACPI backlight brightnes
s control, supported by the ACPI video driver
[ 5.192709] thinkpad_acpi: Disabling thinkpad-acpibrightness events by defaul
t...
Ok, I just discovered the root cause of this issue and it’s already documented in Launchpad:
I guess the conversation can continue there, thanks for the assistance anyways.
Found work around for -28: add “i915.enable_dpcd_backlight=0” to boot parameters
steps, as root or sudo
edit /etc/default/grub adding the parameter to the end of this line, like so:
GRUB_CMDLINE_LINUX_DEFAULT=“quiet splash i915.enable_dpcd_backlight=0”
run update-grub
This has worked for me. The laptop at hand is quite old, its Hewlett-Packard HP EliteBook 840 G2, Kernel Version: Linux 7.0.0-28-generic
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