The correct option is The suspended account will still appear in the user directory.

Suspending a user removes their ability to sign in and stops their access to products while keeping their account record intact. The account remains in the site user directory and historical content such as comments and issue history still reference that user.

The suspended user will still be able to sign in to the Confluence site is incorrect because suspension prevents sign in across the site and across products linked to that account. A suspended user cannot authenticate to Confluence or Jira.

Other users can still mention the suspended account with an at sign is incorrect because suspended users are typically excluded from user pickers and mention autocomplete. Users cannot be newly mentioned via the at sign once they are suspended.

The suspended account can still be chosen as an issue assignee is incorrect because suspended users cannot be selected for new assignments. Existing assignments that reference the suspended account remain visible, but you cannot pick a suspended account as an assignee for new or reassigned issues.

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