Comment 2 for bug 1874568

So I think bind9 should've added a Breaks: bind-dyndb-ldap, but we can still add that.

The only short-term solution is to downgrade bind9, not sure if the eoan packages actually work on focal still, but at least they install. First you need to have an entry for eoan main in /etc/apt/sources.list and run apt update:

echo 'deb http://archive.ubuntu.com/ubuntu/ eoan-updates main restricted' >> /etc/apt/sources.list
apt update

and then downgrade bind9:

apt install bind9=1:9.11.5.P4+dfsg-5.1ubuntu2.1 bind9utils=1:9.11.5.P4+dfsg-5.1ubuntu2.1 libbind9-161=1:9.11.5.P4+dfsg-5.1ubuntu2.1 libisccc161=1:9.11.5.P4+dfsg-5.1ubuntu2.1 libisccfg163=1:9.11.5.P4+dfsg-5.1ubuntu2.1 liblwres161=1:9.11.5.P4+dfsg-5.1ubuntu2.1