Exchange online New-MailboxRestoreRequest about transfer archive data

Hi, If an inactive mailbox has an archive mailbox, you can also restore it to the archive mailbox of an existing mailbox. To restore the archive from an inactive mailbox, you have to add the SourceIsArchive and TargetIsArchive switches to the command used to restore an inactive mailbox.
1. Create a variable that contains the properties of the inactive mailbox.
$inactiveMailbox = Get-Mailbox -InactiveMailboxOnly -Identity <identity of inactive mailbox>
2. Display the LegacyExchangeDN of the inactive mailbox so that you can add it as a proxy address to the target mailbox in the next step.
$inactiveMailbox.LegacyExchangeDN
3. Add the LegacyExchangeDN of the inactive mailbox as an X500 proxy address to the target mailbox.
Set-Mailbox <identity of target mailbox> -EmailAddresses @{Add="X500:<LegacyExchangeDN of inactive mailbox>"}
4. Restore the contents of the archive from the inactive mailbox (source archive) to the archive of an existing mailbox (target archive). In this example, the contents from the source archive are copied to a folder named "Inactive Mailbox Archive" in the archive of the target mailbox.
New-MailboxRestoreRequest -SourceMailbox $InactiveMailbox.DistinguishedName -SourceIsArchive -TargetMailbox <identity of target mailbox> -TargetIsArchive -TargetRootFolder "Inactive Mailbox Archive"
5. After the restore request is complete, you can optionally remove the LegacyExchangeDN of the inactive mailbox from the target mailbox. Leaving the LegacyExchangeDN from the inactive mailbox won't affect the target mailbox.
Set-Mailbox <identity of target mailbox> -EmailAddresses @{Remove="X500:<LegacyExchangeDN of inactive mailbox>"}

I hope this helps. Thank you!

Hello Wahzo

I see that you to transfer a soft-deleted mailbox content to a new shared mailbox for review purpose.
Confirm if the mail box is under litigation hold or a retention policy?
If yes, then it is in inactive state.
https://docs.microsoft.com/en-us/microsoft-365/compliance/inactive-mailboxes-in-office-365?view=o365-worldwide
Confirm if this archive is in the on-premises exchange or in exchange online?

Please note that Shared mailboxes does not have archive unless it has a MS license that contains Exchange online plan 2, and have a default size of 50 GB which can be increase by adding a license that contains exchange online plan 2

If you are restoring from on-premises
Restore to Exchange Online archive mailbox: TargetMailbox is the ArchiveGuid value of the target Exchange Online archive mailbox
https://docs.microsoft.com/en-us/exchange/recipients-in-exchange-online/delete-or-restore-mailboxes#restoring-disconnected-on-premises-mailboxes-to-exchange-online

However I think you need to go through this documentation below.
https://docs.microsoft.com/en-us/microsoft-365/compliance/recover-an-inactive-mailbox?view=o365-worldwide

NOTE
What's the main difference between recovering and restoring an inactive mailbox?
When you recover an inactive mailbox, the mailbox is converted to a new mailbox, the contents and folder structure of the inactive mailbox are retained, and the mailbox is linked to a new user account. After it's recovered, the inactive mailbox no longer exists, and any changes made to the content in the new mailbox will affect the content that was originally on hold in the inactive mailbox. Conversely, when you restore an inactive mailbox, the contents are merely copied to another mailbox. The inactive mailbox is preserved and remains an inactive mailbox. Any changes made to the content in the target mailbox won't affect the original content held in the inactive mailbox. The inactive mailbox can still be searched by using In-Place eDiscovery, its contents can be restored to another mailbox, or it can be recovered or deleted at a later date.