If it isn't already. To check just type
echo $PATH
at a command prompt. The last Ayufan Buster image I grabbed doesn't have it. dpkg-reconfigure is there but not in your path so it doesn't work. You could run it as /usr/sbin/dpkg-reconfigure except it also calls itself which won't work that way.
I just used it to set locales, it does a couple things as well like keyboard layouts, time zones. To see what you're missing by not having it in your path do
ls /usr/sbin
echo $PATH
at a command prompt. The last Ayufan Buster image I grabbed doesn't have it. dpkg-reconfigure is there but not in your path so it doesn't work. You could run it as /usr/sbin/dpkg-reconfigure except it also calls itself which won't work that way.
I just used it to set locales, it does a couple things as well like keyboard layouts, time zones. To see what you're missing by not having it in your path do
ls /usr/sbin