You could still create groups as before, with Ctl + G. This will create a group
with a single visible collection.
However you can also create a group from an existing collection. Just go to
the menu you get in the outliner when clicking in a collection and pick
"Create Group".
Remember to instance the group afterwards, or link it into a new scene or file.
The group and the collection are not kept in sync afterwards. You need to manually
edit the group for further changes.
