I believe you would have to set up a request attribute to capture the x-dynatrace header value and search for this attribute. Once you have this configured you should be able to look in the individual service or use diagnostic tools "top web requests" to search all available purepaths.
Here is a link to the doc that shows how to configure request attributes:
is this still the current state of affairs? It would be really helpful, in a rather large and decentralized organisation, to have the ability to search for x-dynatrace header in the DT UI out of the box - as different point of entry if you will, to start a root cause investigation. E.g. you got logs from your mobile application or a microservice with the x-dynatrace header and want to find now the related PurePath and thus be able to do backtracing and so on.
A start would be simply adding it in the tracing section, similar to the W3C trace ID
May I ask what's exactly the use-case?
If the use-case is to identify a transaction based on some logs (e.g. HTTP header logging x-dynatrace), then wouldn't the Trace-ID already fulfill exactly that use-case?