Recovering 'On my Mac' mailboxes after Mac repair and iCloud restore

Apple recently had to repair my Macbook Air M4, Tahoe 26 and in so doing, wiped the entire hard drive. In restoring my files back from iCloud, I notice that while the mail is all downloading properly, the mailboxes I had set up under the "On my Mac" tab are all gone. Any way to get them back? I couldn't back it up properly because the Mac wouldn't even turn on, so I really have nothing from which to back it up except an old back up from my old Mac in March 2025.

Thanks for any help you can provide.

[Re-Titled by Moderator]

Original Title: "On my Mac" Mailboxes