I see you've mentioned using a VPS for this. Suppose I want a DoH server for private use; is there a reason for me not to host it on my homeserver instead? I suppose my ISP could see the server's DNS queries, but so could the VPS provider, and precaching Cloudflare's top 20k domains seems to provide some level of obfuscation anyways.
I am doing exactly that. I have Unbound running on my firewall/router running Alpine Linux and everything talks to port 443 (DoH). I only set up public DoH servers when people are asking for one or if I am going to be out and about. I had one set up as a demo but there was not much interest in it so I nuked the VM and just left my how-to document in place.