apt update && apt full-upgrade
sed -i 's/bookworm/trixie/g' /etc/apt/sources.list
find /etc/apt/sources.list.d -type f -exec sed -i 's/bookworm/trixie/g' {} \;
# Hold mdadm if it's in use
# apt-mark hold mdadm
apt update && apt full-upgrade
# unhold mdadm
# apt-mark unhold mdadm, then upgrade the rest
# apt update && apt full-upgrade

reboot

apt autoremove && apt clean
apt modernize-sources
#Caveat that trixie-backports might not have a Signed-By on some 3rd-party mirrors. You can fix this by manually setting Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg in /etc/apt/sources.list.d/debian-backports.sources

Deb13 uses tmpfs, so old files may still be in tmp directory. Check and remove

mkdir /mnt/tmp-chk
mount --bind / /mnt/tmp-chk
ls -lha /mnt/tmp-chk/tmp/
# remove files
umount /mnt/tmp-chk
rm -rf /mnt/tmp-chk