Ah, apparently now (RFC8484) it's standardized to use DNS wireformat, but originally Google DNS implemented "DNS-over-HTTPS" to be JSON[1] on 4/2/16 and added DNS wire format on 6/27/19[2].

Cloudflare also has the JSON format available[3]

[1]: https://groups.google.com/forum/?fromgroups#!topic/public-dn...

[2]: https://groups.google.com/forum/?fromgroups#!topic/public-dn...

[3]: https://developers.cloudflare.com/1.1.1.1/dns-over-https/jso...