Extending the default restoration time period in SharePoint Online more than 14 days

To add to Vasil's point, the default retention time for deleted items is 14 days in Exchange Online. You can amend this to a maximum of 30 days:

Set-Mailbox -Id "Some Mailbox" -RetainDeletedItemsFor 30

You can also use the Set-MailboxPlan cmdlet to change the default from 14 days to anything up to 30 days.

This setting controls the time deleted items spend in the Recoverable Items folder before they are permanently removed from the database (unless on hold).