See lots of threads in the support forums on OBS Studio function when the application is started (opened) while there are video sources enabled in one of the Scenes. Encoding is taking place creating -- Preview window compositing (or processing video in background for prep of a Scene change)... irrespective of whether outputting that video composition to a Stream and/or Recording. It surprises me that people think that Recording or Streaming is computationally demanding... it isn't. It is the compositing to be ready to be ready to Stream or Record that takes the effort ... and that distinction is critical
If this is a specific support request, then you should read and follow pinned posts in the forums, and post this, along with an appropriate OBS Studio log, in the right Operating System forum
