I recently conducted some research into DNS over HTTPS (DoH) that is documented here. When it came to identifying any publically available DoH servers available on the Internet I found the best resource to be the curl wiki page to be the best place to start and is probably the most well maintained resource.
I found a few more so I have merged them into the below list and also put together a simple script to do a test GET query against each resolver.
Below is the list of potential endpoints:
The test script is available at the below URL: https://gist.github.com/dtmsecurity/a849e985e6a0b61aeb54890ebcfa55eb
If you run the script you will see that a small number resolvers do not support GET style queries.