Most of my infra is Debian, and I did it without serious incident:

#Update everything to latest
apt update && apt upgrade && apt full-upgrade && apt --purge autoremove
reboot

#Verify that debian_version is 12.x (STOP IF NOT 12!)
cat /etc/debian_version

#Check for any pinned or held packages
apt list '?narrow(?installed, ?not(?origin(Debian)))'
apt-mark showhold

#Swap bookworm for trixie in repo files
sed -i 's/bookworm/trixie/g' /etc/apt/sources.list
sed -i 's/bookworm/trixie/g' /etc/apt/sources.list.d/*

#Carry out update
apt update
apt upgrade --without-new-pkgs -y
apt full-upgrade -y
reboot

#Verify that debian_version is 13.x
cat /etc/debian_version

#Modernize apt sources to v3
apt modernize-sources -y

And then maybe apt update to make sure the updates still work OK.

Sometimes you have to make changes to certain repos that don't have Trixie manifests, but that's easy enough to roll back.