I’m interested in the same thing (both query upstream DNS over HTTPS servers, and answer to DoH queries), but using dnsmasq. I haven’t had much time to look into this yet, but will definitely try to implement it later, so any recommendations would be appreciated. So far my research notes on this topic only contain:

https://wiki.archlinux.org/index.php/Dnscrypt-proxy
https://packages.debian.org/sid/main/nss-tlsd
https://packages.debian.org/sid/main/tlslookup
https://blitiri.com.ar/git/r/dnss/b/master/t/f=README.md.html

Do you want Unbound to query upstream DNS over HTTPS servers or do you want unbound to answer to DoH queries?

For the former, unbound cannot query upstream DoH servers, only DoT and DNS at the moment. An issue is still open for setting DoH as upstream. A solution is to use cloudflared or dnsproxy to proxy DNS queries to DoH upstream servers.

As for the latter, unbound can be set to answer to DoH queries.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I’ve seen in this thread:

[Thread #111 for this sub, first seen 6th Sep 2023, 05:45] [FAQ] [Full list] [Contact] [Source code]

Are you using the Unbound built into OPNsense, or something else? I ask because it’s easy to configure Unbound in OPNsense for DoT. If your ISP isn’t blocking DoT it will be just as secure.

And yes, it will be much more private. Right now if you’re using neither DoT or DoH your ISP will be able to see all your DNS requests in the clear. With either of the above it will be encrypted and they will not be able to read them.

Better to use DNS over TLS instead since I think it supports that natively.

If you use a privacy focused DNS server it would help a bit since it stops your ISP from being able to see DNS lookups.