I have submitted a bug report to Unbound on Github. If you are also experiencing this issue and have anything to add that I didn't include, please share a comment or comment directly to Unbound on Github.
I've tried reinstalling Unbound, but the issue persists. My setup follows all OPNsense instructions for setting up DNS over TLS. DNS traffic flows over the service and the DNSBL is working but the upstream DNS traffic is unencrypted. No DNS servers are set anywhere else in OPNsense and I have a firewall rule blocking outbound DNS on port 53. The firewall shows DNS traffic going out to the port specified in Unbound.