https://dnscrypt.info/faq/ states for both DNS over HTTPS and DNS over TLS that it
Provides more information than regular DNS to resolver operators in order to fingerprint clients
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TLS Resumption is a mechanism which allows the client to resume a recent TLS session so they can use the previously established session keys to continue encrypted communication and skip the key exchange step in the TLS handshake. However, it also allows sessions to be linked together by the server, so it can be used to track the client over longer periods of time.
A similar problem is presented by TCP Fast Open. Clients can send a TFO cookie to reduce the round trips required to open a TCP connection. However, like TLS resumption, this can be used to uniquely identify the client and track it across sessions.
Another way to fingerprint clients would be through User-Agent, Accept-Language and Cache HTTP headers to infer information about the client such as the client version, locale and possibly some information about a subset of the client's history, as mentioned in RFC 8484.
Of course, it's possible to mitigate most of this on the client side, by not utilizing TLS resumption or TCP fast open, and not sending accurate HTTP headers, perhaps even randomizing them (although I am not sure whether any DoH/DoT clients take care of this or not).