Loki derived fields and correlation between logs and traces

I want to correlate my Loki logs with my traces from Zipkin or Jaeger. Unfortunately, I can’t find an example / explanation which explains the procedure end-2-end (I have Grafana 7.4.0.)

This article talks about generating a derived field for a trace-id,which should somehow wire together loki logs with traces via generated hyperlinks:

I tried so and created a derived field “trace_id”, which grabs the value of the traceId from the incoming log statement via pattern matching. I also added an internal link to zipkin and jaeger:

But when going to Explore Loki or Explore Jaeger / Zipkins, I don’t see any generated hyperlink, although both Loki and Jaeger / Zipkin have the same traceId.

What’s the rationale for that derived field? Which name should it take? Where is it referenced for log / trace correlation? Can it be given any name?
What should the query string look like? Is ${__value.raw} correct and what does it mean?

Does regex have to match the “raw” log message from the app under monitoring, or does it have to match the already parsed format (by Promtail)? The first is an unparsed on-liner statement, the second is key-values parsed result? Do the key for the traceid / traceID / trace_id between loki derived field and promtail parsed field need to match ?

I also added a connectivity the other way round from Jaeger / Zipkin to Loki, but that also does have no effect:

Thanks a lot!