Export all parts of an email account

I would like to export my email account from Apple Mail to serve as a backup. I followed the directions at https://support.apple.com/guide/mail/import-or-export-mailboxes-mlhlp1030/mac

However, this seemed to only work on the Inbox, and not Sent mail, Archived mail, etc. Also, the read-status of the emails was not preserved as far as I could tell when I re-imported the export to check on it.

1) I assume I could export each category of mail (inbox, sent, archived) separately, but is there a way to combine into a single MBOX file so that they don't get accidentally get separated years from now?

2) How do you preserve the read-status of the export?

3) Bonus: Can you create an export that does not include attachments?