Importing Time Machine backup from MacBook Pro with High Sierra?

I found the Import option in the File menu. After setting up Mail properly. I imported the small box and now waiting for the big one. I expect the 'read status' and the link to attachments to disappear. Let's see...

It did something. I placed the contents of the old Mail folder inside the Mail folder and gave permission to overwrite existing, empty after all, folders (Maildata I think).

Then I started Mail and the message appeared that it was importing mail. Nothing appeared, but all mail was now moved to a new folder called V5. The content also a new location. The folder Mailboxes is 8KB in size, consider it empty. In Maildata there is stuff that is old, as expected. There are two other folders with a name starting with POP and a 3rd RSS (a pity that feature is dropped). The two POP-folders are 5.51Gb and 1.58Gb in size respectively.

Manually moving those inside the folder Mailboxes (and restarting Mail) did not do it. Mail still does not show them.

Should I first make the two POP-accounts in the settings?

I have the feeling I am only one step away from solving this, but what to do next?

TIA!

So in theory I could move the contents of the backup in Library/Mail to /Library/Mail/V2 and import at launch of Mail would pick it up from there?