As per my understanding in both scenarios we write our research addressing the research community. Yet at what point we decide to write a conference paper or a journal paper? Is it via looking at the target audience. If so what are the differences in the audience?
The issue is not just the "audience", but rather the "visibility".
Any venue - be it a journal or a conference - has some specific topics that define the "expected audience" of the people that will read the articles published within it.
However, in conferences you know in advance that at least N people will look at your work, because it has to be presented to the people attending the conference (at least before Covid - with online conferences, I had the impression that everyone was attending just for making their own presentation, and then go do something else). These people will mostly be researchers, but there will also be practitioners.
Because of this reason, there are different styles that must be adopted when deciding if the paper is going to be published in a journal or a conference. In conferences, you are usually restricted by the amount of available space, and it is important that the "claim" of the paper will make an impact now, or that will at least raise the interest of the people attending the conference; this may favor a more "high-level" approach on a trendy topic, where technicalities are not as crucial.
On the other hand, in journals you have more space available, meaning that you can go more deeply in discussing the technical details of your proposal. This may make the paper more interesting for future and long term research.