I haven’t found a way to filter the outliner for hidden geometry.
I know that hidden stuff is greyed out, but if you have a massive model with hundreds of entities, scrolling and spotting grey lines becomes cumbersome.
Is there a way to filter for hidden geometry in the outliner ?
Not excactly the answer to your question, but an alternative way…
With Thomthoms selection toys, you can select everything (hidden geometry turned on) and choose “select only → hidden” to reduce the selection to all hidden geometry… (not within nested objects)