Your upstream DNS server is blocking this domain. You will need to change upstream DNS servers if this continues to be blocked by the one you are using. Here are my results:
**root@nanopi** : **~** # dig +short archive.is @8.8.8.8
94.16.117.236
**root@nanopi** : **~** # dig +short archive.is @1.1.1.1
0.0.0.0
**root@nanopi** : **~** # dig +short archive.is @9.9.9.9
0.0.0.0
If Pi-hole is not blocking the domain, then adding it to the whitelist will have no effect. What is the output of the following command from the Pi terminal:
pihole -q archive.is