I think I figured it out. It is the "Local Network" privacy setting on Mac. I had it set to off on Chrome and Firefox, it seems like it's default enabled for Safari. Once I switched it on, I could access. it.
Posting here for completeness, thanks for the response rdwebdesign
In between now and the post, I reconfigured pihole, thus the two IP addresses
hostname -I returns 192.168.2.52 192.168.2.51 fd2f:65f7:58a1:c44d:a3f8:d43:48a:7fd9 fd2f:65f7:58a1:c44d:2a81:ef7f:55ba:d2f
debug code NTa6QAdX/
nslookup pi.hole
nslookup pi.hole
Server: 192.168.2.1
Address: 192.168.2.1#53
Non-authoritative answer:
Name: pi.hole
Address: 143.244.220.150
nslookup pi.hole 192.168.2.51
Server: 192.168.2.51
Address: 192.168.2.51#53
Name: pi.hole
Address: 192.168.2.51
nslookup 192.168.2.51
Server: 192.168.2.1
Address: 192.168.2.1#53
51.2.168.192.in-addr.arpa name = pihole.
nslookup pi.hole 192.168.2.52
Server: 192.168.2.52
Address: 192.168.2.52#53
Name: pi.hole
Address: 192.168.2.52
nslookup 192.168.2.52
Server: 192.168.2.1
Address: 192.168.2.1#53
** server can't find 52.2.168.192.in-addr.arpa: NXDOMAIN