Since a few days/weeks I couldn’t get images from catbox.moe when I was using my WiFi with pihole. The reason was that the default DNS Quad9 (filtered) was blocking it.
It took me a while to figure out how pihole actually sets the DNS.
So in the Web you go to settings and then to DNS and then tick in for example Google.
The problem wasn’t in the lists. It was in the default choice by the truenas pihole docker. There it has Quad9 (filtered) as a default.