There is discussion about that problem on Manjaro forum.
Seems like users affected use Pamac for system update.
It is always recommended to update your system from command line… either by pacman or yay.
sudo pacman -Syu
yay -N #to update only packages from official repos
yay #to also update AUR packages
what should I do to update the kernel from 6.1.159.1 to Linux 6.12.63-1-MANJARO as Muzqs said till seems to have the issue regarding add/remove
If you want to install a new kernel and edit bootmenu.
sudo manjaro-settings-manager
Edit these lines in /etc/default/grub as root.
sudo nano /etc/default/grub
GRUB_TIMEOUT=5
GRUB_TIMEOUT_STYLE=menu
This gives a delay of 5 sec and shows you the menu.
After these change you need to update grub like
sudo grub-mkconfig -o /boot/grub/grub.cfg
or
grub-update
Reboot system into desired kernel.
ps: and as @napcok said try to avoid Pamac gui and use terminal command instead to update your system.
FYI
It is not a Pamac issue perse (i think).
All root GUI are affected. Like pkexec did not work too.
root login for password got shakie on the screen and disappears.
Personally I think wait for fix and install another kernel 
ps: I never use pamac, always cli updates. and still got this issue.
This where I change timeout seconds is this correct?
GRUB_TIMEOUT_STYLE=menu - Shows the menu automatically ( this should be changed =10)
GRUB_TIMEOUT_STYLE=countdown - Shows a countdown timer ( this should be changed =0)
GRUB_TIMEOUT_STYLE=hidden - Hides the menu (press Esc to show it) (This should be changed =-1 )
after Save the file (Ctrl+O, Enter, Ctrl+X in nano)
sudo grub-mkconfig -o /boot/grub/grub.cfg
but to change to should the kernel I should do: sudo nano /etc/default/grub
GRUB_TIMEOUT=5
GRUB_TIMEOUT_STYLE=menu
bootmenu and installing kernel.The bootmenu part is just to make it easier for you to select a kernel at boot.
The menu is disabled by default. That’s why I added it.
Installing a kernel you do with manjaro-settings-manager.
Tip: Invest some time to read about how to manage kernels on manjaro
How to edit grub menu
How to update/install software from the terminal with pacman and yay
In short.
step 1:
step 2: (optional)
RUB_DEFAULT=saved
GRUB_TIMEOUT=5
GRUB_TIMEOUT_STYLE=menu
GRUB_DISTRIBUTOR=‘Mabox’
GRUB_CMDLINE_LINUX_DEFAULT=‘quiet udev.log_priority=3’
GRUB_CMDLINE_LINUX=“”
as you can see I did change as you said but still when I try to change to a different kernel the another image appears on the left side and it shatters all around then it disappears any help
please
I apoligize it worked from the sudo manjaro-settings-manager able to apply a new kernel
updating the kernel to Linux 6.12.63-1 makes everthing work the add and remove and also the manjaro application utility thank for the help
Can confirm, worked for me also. I was plagued with this issue too.