Good one!
I knew about that setting before I configured my Pi so I disabled that one made sure it was disabled.
And only after configured for advertised two DNS servers via DHCP.
I did not take into account that not everyone is aware of that triple DNS server setting.
But still, the grep command I supplied previously would have revealed that as you would see three DNS servers for that option:dns-server directive.
EDIT: On that freshly installed tinker VM of mine:
$ sudo pihole-FTL --config dhcp.multiDNS
false
$ sudo pihole-FTL --config dhcp.multiDNS true
true
$ sudo pihole-FTL --config dhcp.active true
true
$ sudo grep dhcp-option= /etc/pihole/dnsmasq.conf
dhcp-option=option:router,10.0.0.1
dhcp-option=option:dns-server,0.0.0.0,0.0.0.0,0.0.0.0
dhcp-option=option:ntp-server,0.0.0.0
EDIT2: This is weird:
$ sudo pihole-FTL --config misc.dnsmasq_lines '[ "dhcp-option=option:dns-server,0.0.0.0,10.0.0.4" ]'
[ dhcp-option=option:dns-server,0.0.0.0,10.0.0.4 ]
$ sudo grep dhcp-option= /etc/pihole/dnsmasq.conf
dhcp-option=option:router,10.0.0.1
dhcp-option=option:dns-server,0.0.0.0,0.0.0.0,0.0.0.0
dhcp-option=option:ntp-server,0.0.0.0
dhcp-option=option:dns-server,0.0.0.0,10.0.0.4