Find clips not used in a specific timeline

With "Usage" I can display the number of uses for each clip in the media pool.
However I cannot find out the numbers for a specific timeline (or I don't know how to).
I'd like to see which clips are *not* used in a specific timeline.
This is important if I want to use Resolve to "Pre-process" each clip (some effects are only available via the timeline), and I don't want to miss one.

With "Usage" I can display the number of uses for each clip in the media pool.
However I cannot find out the numbers for a specific timeline (or I don't know how to).
I'd like to see which clips are *not* used in a specific timeline.
This is important if I want to use Resolve to "Pre-process" each clip (some effects are only available via the timeline), and I don't want to miss one.

Be careful with that readout. Resolve's "usage" functionality, to put it politely, is not quite there yet.

It will only show you the clip usage in the currently opened timelines, not of all the times it is actually used in your project, and even then sometimes you're going to have to double-check those numbers, because they tend to do their own thing.

It will only show you the clip usage in the currently opened timelines

Does the "Load all timelines when opening projects" option in user preferences affect this?

I'd like to see which clips are *not* used in a specific timeline.

Set your bin view to List and Sort by Usage.

It will only show you the clip usage in the currently opened timelines...

In my experience, at least, this is only partly correct... but that illustrates the point that it can be untrustworthy. The Usage column in the Media Pool list view displays a total usage count for a given clip in the currently loaded timelines (it doesn't matter if its open or closed tho). However, when you right-click on a clip and view the Usage submenu, that only lists those instances of usage in the currently active timeline.

Does the "Load all timelines when opening projects" option in user preferences affect this?

Yes, as it says on the tin, that option will force all timelines (that have not been explicitly disabled) to load on project open, hence all Usage counts should be correct.

I'd like to see which clips are *not* used in a specific timeline.

One way you could use the existing functionality to create the search you need, is to select all clips in a given timeline and add a 'Flag' of a specific color to those clips. You could use a different Flag color for each timeline. Then create and label Search Bins as necessary to filter by "MediaPool Properties Usage is 0" and "MediaPool Properties Flags does not contain <timeline flag color>"... it wouldn't be especially dynamic as you're setting the flag manually, but it could get the job done when necessary.

The other way to do it is to leave the timeline you want to check open & visible in the Record viewer, then close Resolve. When you start Resolve again, the Usage column will show only the clips in that timeline, so zero usage indicates not used in that particular timeline. It's clunky, but it works. It is not a solution to use while editing!