Public Folders can be migrated into other Public Folders or shared mailboxes. You cannot migrate any Source other than a Public Folder, into a Public Folder.
The only Source email system that is supported for MigrationWiz Public Folder migrations by MigrationWiz is On-Premises Exchange or Exchange Online (Microsoft 365). No other Source can be used during Public Folder migration, such as G Suite, Zimbra, or even an Exchange mailbox.