I have just updated to 2.80 from 2.79. When I open a model in which I had some hidden groups they now in 2.80 have the eye icon to show they are not hidden, but they are also semitransparent in the menu. In the scene I don't see any object in the group.
How can I show previously hidden groups etc..?
It might be because they are not displayed in the viewport, click on the key icon on the top and activate the Disable in Viewport icon (monitor icon) to make this option visible in the Outliner, then activate it for the object or collection you want to make visible in the viewport. You'll also need to make sure your objects or collections are visible for render (camera icon this time).
There is an new feature in 2.8, where you can hide objects globally in the viewport. (So you can't unhide them with ctr+h but they show up in the rendered image)