hello, basicallly i am new to manjaro and to linux at all. i installed the last version of kde just yesterday. i got laptop where f1 and f2 make brightness lower and higher, but sometimes but pretty regulary my brightness can get to zero while i am not pressing any of the buttons. also the thing is fn+f1 and fn+f2 makes nothing, but they must. thanks for help!
laptop honor x14plus amd ryzen 7 8845hs+radeon 780m
Please rephrase your topic to use proper English grammar and spelling.
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Doing so ensures that an old dog like me have a chance of getting a proper understanding of your issue.
sorry, just edited
There is a similar issue posted. You may want to try a different kernel and see if it makes a difference.
Welcome to the forum! 
There was a recent report about a kernel regression which may be causing this… 
Given that kernel 7.1 is not a long-term-support kernel, chances are that it’ll be fixed in 7.2.
However, you could try installing the 6.18 LTS kernel and see whether it makes a difference. But in that case, you must explicitly choose to boot into 6.18 each time — using the “Advanced options” in the grub menu — because if you have accepted btrfs as the default filesystem, then grub can’t save its most recently booted entry anymore, and will automatically boot the kernel with the highest version number if the user has not explicitly chosen otherwise.
I’m not sure if my suggestion is really suitable for a beginner. There’s a DKMS kernel module for your laptop’s keyboard on GitHub, and it’s also available in the AUR. You should take a moment to read up on what the AUR is and what the risks are. If you are fine with it:
sudo pacman -S honor-fmi721-kbd-dkms
The OP’s issue is with display brightness, not with keyboard backlight brightness. 
pacman cannot install AUR packages. An AUR helper, such as pamac or yay, should be used instead. To install the package using pamac:
pamac build honor-fmi721-kbd-dkms
Note: sudo should not be used with pamac. It will request authentication via polkit if and when required.
Can you post the result of
inxi -zv8
Formatted as code (the <|> button)?
Thank you for clarifying 
I am thinking, perhaps Huawei Honor came with Microsoft Windows, yes?
Quite a lot of laptops (computers in general) has been built for Microsoft Windows.
As such the hardware may rely on how Microsoft Windows interacts with the hardware.
The brightness is controlled through a hardware interface called ACPI.
To work around this you may need to tweak the kernel by use of parameters to make it behave.
Precisely what parameter I don’t know but it is likely related to the version of Microsoft Windows that came with the system.
The Arch Linux based EndeavourOS has an excellent article on the subject
This laptop might have an ambient light sensor. In the KDE Plasma System Settings inside Display Configuration there is “Automatically adapt to environment” under the Brightness slider. Make sure it is turned off.
coming in next version of Kernel 7.1 (7.1.9 )