The preference Show Other Object While in Edit Mode allows you to choose if you want to see other objects that are outside of the group (group/viewport/symbol/etc.) that you are editing.
It is one of the Quick Preferences that you can add to the Tool bar.
If you turn this preference off, you will not see any objects that are outside the group.
If you turn this preference on, you will be able to see all the objects that are outside the group, but they might be show in grey.
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