An employee cannot enter time as no activity item is showing in the drop-down. However, this employee is able to enter time on the Core Mobile app.
If you are unable to see any items in the drop-down lists for, say, Activity Items or Projects, and there is no change in the assigned security permissions, this might be a data filtering issue. Go to User Preferences and reset your filters. You should be able to see the relevant items in the drop-down lists.