Can you post results for below two on the Macbook:
nslookup debianserver 192.168.1.100
nslookup debianserver
And on Pihole:
hostname -f
cat /etc/hosts
cat /etc/pihole/local.list
If you have dhcpcd5 installed that comes with Pi-hole:
pi@noads:~ $ apt policy dhcpcd5
dhcpcd5:
Installed: 1:6.11.5-1+rpt7
Candidate: 1:6.11.5-1+rpt7
And active:
pi@noads:~ $ sudo service dhcpcd5 status
[..]
Active: active (running) since Sun 2019-09-08 22:28:43 CEST; 1 weeks 0 days ago
[..]
IP settings belong in /etc/dhcpcd.conf:
pi@noads:~ $ tail /etc/dhcpcd.conf
[..]
interface eth0
static ip_address=10.0.0.2/24
static routers=10.0.0.1
static domain_name_servers=127.0.0.1
And /etc/network/interfaces should resemble below:
pi@noads:~ $ cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback
iface eth0 inet manual