There are 4 types of graphs:
Active - useable graph
Archive - kept and can be retrieved at a later date
Delete - gone forever
Hidden - doesn't show up in search or data entry but can be used as part of the formula in a calculation graph or as the Key Result of an Objective.
Active and Hidden graphs are used to calculate your monthly subscription value. Archived graphs are stored for free and do NOT count against your monthly subscription.
How to Hide a Graph
Go to Edit Graph settings via the 3-dot menu and check Hide Graph in menu.
When you want to find Hidden graphs see How to Find all Graphs Types.