Litigation hold and In-place hold are transparent to the user, so they will not know they are on hold.

What does litigation hold do in Office 365?

An Office 365 litigation hold suspends any retention policy or automatic deletion for a given mailbox so that no ESI can be removed from the mailbox. Important: To be put on litigation hold, a mailbox must be assigned either an Exchange Online Plan 2 license or a separate Exchange Online Archiving license.

How does a legal hold notice work?

A legal hold (also known as a litigation hold) is a notification sent from an organization's legal team to employees instructing them not to delete electronically stored information (ESI) or discard paper documents that may be relevant to a new or imminent legal case.