After upgrading to v6 (docker), I noticed my client received the pihole docker network address as the DNS server due to a dhcp-helper in my setup. After troubleshooting, I found that dhcp-option=option:dns-server,192.168.x.x was ignored.
A quick look at pihole.toml led me to this post for a solution
Is there another way to pass this option, or do we need to manually re-enable it and leave it ?
add an environment variable (FTLCONF_misc.dnsmasq_d) to your compose file, to enable this option;
start the container without it and execute the command from the other post to enable misc.etc_dnsmasq_d;
start the container without it and use the web interface to enable the misc.etc_dnsmasq_d option (see image - left side);
don't use misc.etc_dnsmasq_d option and don't use a volume external files for dnsmasq.
In v6, you can enter dnsmasq options via Web Interface using the new misc.dnsmasq_lines (see image - right side).