Deafened

A creature suffering the Deafened condition can't hear and loses any ability to perceive sound.

No hearing: You can't hear anything. You're cut off from spoken communication, alarms, footsteps, and other audible cues.
Auto-fail hearing checks: You automatically fail any ability check that requires hearing (for example, a Wisdom (Perception) check made to notice a sound).

That's the full extent of the condition. Deafened on its own imposes no penalty to attack rolls, saving throws, or your AC, and it doesn't affect your movement, actions, or ability to speak and cast spells. Note, however, that it can prevent effects that rely on you hearing them: you can't be affected by anything you must hear (such as a spoken command or a sound-based trigger).