After upgrade to 15.4 the key combinations for keyboard backlight, doesn't works anymore

on my son’s laptop CLEVO NS50MU linux ultrabook after upgrade from 15.3 to LEAP 15.4 with KDE the key combinations Fn+keys on the numeric keypad, doesn’t works anymore, the combinations Fn+F1 or F2 and other works, with 15.3 they worked.
what I can do to have the keys for keyboard backlight working?

I met with something similar in the past, possibly due to bad compatibility of the firmware (aka BIOS) code in some laptops and the kernel.
You may try to add 'acpi_osi= ’ to the kernel boot command line so that it looks like, for instance:

linux /boot/vmlinuz-5.14.21-xxx-default root=yyy splash=silent quiet acpi_osi=

To try that hit “E” at the GRUB screen, search and edit the relevant line and then hit F10 to boot.
If it works, a permanent fix is editing the “GRUB_CMDLINE_LINUX_DEFAULT=” line of file /etc/default/grub and then run ‘grub2-mkconfig -o /boot/grub2/grub.cfg’ to update grub.cfg
If interested you may find further details in the kernel documentation, for instance here

I own a TUXEDO notebook (which is a CLEVO P65x sold by TUXEDO) and I need a special kernel module called tuxedo_keyboard to get the keyboard backlight switches working.

Check with CLEVO (or your notebook dealer) if you can get the sources for such a module.

I got mine from here (if you are lucky they will work for your son’s notebook as well).

manythanks, it was tuxedo_keyboard that was installed but it seems to need also this
tuxedo-keyboard-kmp-default - TUXEDO Computers Kernel Module
taken from here obs://