“There appears to be a bug in macOS Sequoia causing some requests to bypass the installed DNS proxy and be sent unencrypted to the system’s default name server instead.”
Little Snitch blamed macOS Sequoia, reported it to Apple and warned that any DNS proxy was exposed. The next day it found the bug only hit its own 6.1 proxy and shipped 6.1.1 that afternoon. Users who turned on encrypted DNS had some lookups going out in the clear, Firefox included. The vendor checked Apple’s code before its own.