It has been known since December last year that 6.5 is EOL and a prominent notice in the stable announcement comment number 2 - the Known Issuess comment.
There is a lot of jokers in this - no guarantee it will work in first try
First thing to try is to boot into linux65 → then use mhwd-kernel to install linux66 and in the same execution remove the current kernel.
sudo mhwd-kernel -i linux66 rmc
You are likely to be greeted with information about outdated system - continue anyway.
If successful - reboot the system and rerun
sudo pacman -Syu
Otherwise you will need to remove the gpu drivers
sudo mhwd -r pci video-nvidia
Then sync system with linux66 → install gpu drivers
sudo pacman -Syu linux66
sudo mhwd -i pci video-nvidia
Or you can do it the tough way
sudo pacman -Rdd $(pacman -Qsq nvidia-)
Then sync system with linux66 → install gpu drivers
sudo pacman -Syu linux66
sudo mhwd -i pci video-nvidia
Finally reboot
reboot