Need to restore user created Mac mailboxes

Unfortunately, the later versions of macOS (Catalina+) have removed the ability to restore email mailboxes via the Time Machine interface. However, it still may be possible to access them from Time Machine backups, but will require using the Finder app to locate them.

Here are the basic steps:

1. If running, close the Apple Mail app.
2. Open a new Finder window: Finder > File > New Finder Window
3. To view hidden files, use the <cmd><shift><period> key combination. Note: They don't need to be held down simultaneously.
4. Select your Time Machine backup drive from Finder.
5. Open: Backups.backupdb > Your Mac's Name > The backup folder with the date you want to restore from > Macintosh HD or Macintosh HD - Data (on Catalina+) > Users > Your User Name > Library > Mail > Vx (where x = 10 for Ventura)
6. Copy (NOT move) the entire V10  folder somewhere on your Mac, preferably somewhere not syncing with a cloud service. A good place would be the Downloads folder.
7. Open the V10 folder you just copied to the Downloads folder. You’ll see a bunch of alphanumeric folders ... one for each email account and one for the "On My Mac" mailboxes. Open each one until you find the mailboxes you’re looking for. Be sure to note the directory path to where it is located.
8. Open the Mail app.
9. Choose File > Import Mailboxes, navigate to the noted location
10. Choose “Import as Apple Mail”.
11. Next, in the Mail app, you’ll see a new “Import” folder, maybe with another sub folder. Your mail should be in there.

70+? Not too far behind you, as are a number of others here at the ASC. I'm glad those steps help you get back those mailboxes. Not sure why Apple removed the much simpler way via the Time Machine interface, but I believe the rational was to put the onus on the email providers ... funny that Apple is one of them.

... and "kid in a candy store." That brings back memories of the local "mom & pop" grocery that I frequented. Had a large glass display with just about every type of candy a kid would crave. Spent many a penny there. Had to do a lot of paper routes. ;)