If you mean to hide media that has been on the timeline but no longer is on the timeline, then in Project media click on the cube in the top LH corner of the Project Media window:
Doing so, removes from the Project Media listings any media that isn't on the timeline at the time of clicking.
I would actually like to only view media which hasn't been used on timeline, while some media is already in use it would be nice for a workflow aid it would be nice to remove already used media from the view
Well, that's the whole point of the Project Media window, that it shows what's being used in the project. But you could switch the "View" to "Details". This listing shows how often which media is used in the timeline. Use the sort function in the title bar to quickly find out what you haven't used yet.
I have to agree with you that it would at least be nice to see clearly in the "Thumbnail" view what has already been used and what hasn't. I seem to recall that in Pinnacle Studio, the media used was marked with a green check mark.
@Steven-S - There’s a much underused Search Feature within our Project Media Pane. You can Search for Used and apply a search criteria do “0” that’s a ZERO. It will then deliver a New Bin full of unused Media which you can then Thumbnail to view! I’m addicted to this hidden feature….. addicted.
@walter-i. yes, Pinnacle Studio adds a green check mark to show when media is used. And it also has "padlocks" in the track header to lock the track. Hoping Vegas will get them sooner than later.... 😉