Re: Debian ships sysv init, it's not enabled by default
While I haven't had a chance to look at Bullseye yet, given that it just came out, I assume that the normal Debian installer still doesn't give a choice of the initial init system and forces systemd. However, since they are now saying they have better support for sysvinit (yay!), I imagine the same steps I've been following since Jessie will apply.
After initial boot:
apt-get install sysvinit-core
apt-get purge systemd
Create /etc/apt/preferences.d/systemd-blacklist to keep systemd init away:
Pin: release o=Debian