3D Viewport:
- Shift-H - isolate active item(s)
- alt-H - unhide all items
- Control - H: Isolate menu
- From this menu, you can use the listed hot keys to isolate a collection.
- Pressing Shift- will isolate that collection in addition to other isolated collections
- Pressing number keys on main keyboard does the same thing (as does shift-number)
Alt h does not unhide objects if another collection is isolated.
Outliner:
Holding shift and clicking a collection’s eye will toggle its children as well
Also, when it comes to isolating a select number of objects, local view is your friend.