FTL issues: Connection refused. Is FTL running?

[deHakkelaar]

You still have your router configured on the clients for DNS resolution and not Pi-hole's IP.
With the first nslookup, the Mac is querying the router 192.168.1.1 and not Pi-hole 192.168.1.19 like in the second nslookup.
Need to fix that first by configuring DHCP on the router or if not possible, disable LAN DHCP on the router and enable the DHCP service on Pi-hole:

How do I use Pi-hole's built in DHCP server (and why would I want to)?

Using Your Existing Router For Network-wide Ad Blocking You might not need to use Pi-hole's DHCP server: In many home environments, your router also functions as your DHCP server. In this case, you can often set Pi-hole to be the DNS server for your network clients in the router's DHCP (or LAN) settings page, which allows all of your network clients to block ads simply by connecting to the network. Setting it up this way is also what makes Pi-hole very powerful for network-wide ad blocking. …

EDIT: Not sure if works on a Mac but below one displays DNS server(s) used on Linux clients:

cat /etc/resolv.conf