apt update && apt upgrade && apt dist-upgrade && apt --purge autoremove
apt full-upgrade

sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list
#sed -i 's/non-free/non-free non-free-firmware/g' /etc/apt/sources.list

apt update
apt autoremove
apt clean
apt upgrade
apt dist-upgrade
apt full-upgrade
apt autoremove

#apt install nvidia-driver firmware-misc-nonfree

reboot

$ cat /etc/debian_version
12.1