Last year, OONI wrote a research paper ("Measuring DoT/DoH Blocking Using OONI Probe: A Preliminary Study") which was presented at the Network and Distributed System Security Symposium (NDSS'21) as part of the DNS Privacy Workshop. You can read this paper here: https://www.ndss-symposium.org/wp-content/uploads/dnspriv21-02-paper.pdf
This study involves an investigation of encrypted DNS (DoT & DoH) blocking in Kazakhstan, Iran, and China with a new OONI Probe experiment (DNSCheck).