"_81._https.pi.hole" in query log

Received queries are outside of the control of Pi-hole, and I would not classify this as expected behavior. The client is requesting that domain, and Pi-hole is receiving and processing the request.

The domain does not exist, and Pi-hole correctly returns that result.

Note that these are Type HTTPS queries, not A queries. There is some discussion about this query type in this thread and the referenced link: