Yes, there is. I pinged DL6ER above. He gave the instructions to a user once, I'm fairly sure about it. I just cannot find it right now. He will know what to do.
That's for DoH between the Pi-Hole and the DNS provider though - so upstream, right?
(on a sidenote, I used Cloudflared at first when I started using Pi-Hole, moved to Unbound later)
What I had in mind is to keep using Pi-Hole + DNS, and have the devices see the Pi-Hole as DoH source - so downstream.
Makes sense I hope...
Unfortunately, you git this wrong. I wrote a guide how to use Pi-hole with any upstream DNS server using https-dns-proxy in the past. This was not about a downstream connectivity.
In contrast to
using https-dns-proxy is not a cloudflare-dependent solution but, instead, vendor-independent which is better IMO. When I find the time, I will summarize my steps a long time ago. I only described it for another user and don't run this myself, so I'd have to dig out the details, first (I'm using a local unbound solution).
Sorry, I read your post as a request for an upstream proxy.
But regardless of upstream or not, let's keep this focused:
Running a DoH server will not allow you to block DNS-over-HTTPS, which was the original request.
I'll split your question for running DoH in front of Pi-hole into a separate topic for discussion. 
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