You want to see two things at once, clearly and separately:
Playlist Preview: A dedicated window that shows you the clip you’ve selected from the playlist, playing it back in its original, unedited state. This lets you quickly review your raw footage.
Timeline Preview: A separate, dedicated window that shows you the portion of your video that’s currently on your timeline, with all your edits and effects applied. This is your “final output” preview.
I have tried to implement this, but I have faced technical difficulty between the UI library we use and the way we display video. That is why a couple of years ago I had to drop support for external monitoring using a system monitor. You need to use a Blackmagic Design HDMI or SDI peripheral now. There is surely a way to do it (including separate previews), but I have been choosing other battles. Still, I agree and accept this suggestion.
I don’t understand what you say about the use of the Blackmagic Design HDMI or SDI peripheral. But I have full hope in the software, I know sometime in future they will be a way to do it