Once moved to Microsoft 365, Archived email is now available through Outlook as an Online Archive mailbox. This additional mailbox can hold 100 GB of archived emails.
Any Mail over 2 years old will automatically move to the Archive Mailbox in the same folder structure as your standard mailbox. The Archive Mailbox will hold all emails that are between 2 and 10 years old.
Once an email is over 10 years old it will be automatically deleted and unrecoverable.
You will see this mailbox, listed as Online Archive-Username, at the bottom of your available Mailboxes in Outlook below your Inbox or as In Place Archive - Username if using a web browser to access your mail online.
Outlook Client View
Web Mail Client View