IOS14 Apple Mail Upgrade Irretrievably Deleted my iPhone POP3 Mailbox Data. YEARS OF MAIL NOW GONE.

Apple Mail has lost my iPhone mail data stored in iPhone local POP3 mailboxes.

NB The data IS NOT available from the POP3 email servers. As per the Post-Office Protocol the mail is deleted from the mail server after retrieval and being 'safely' stored in a local POP3 mailbox on the iPhone.

I upgraded my iPhone to IOS14 (14.0.1) and the Apple Mail program appears to have created new local POP3 mailbox files without keeping the pre-existing iPhone POP3 mailboxes with several years of previously downloaded mail.

My mail data appears now to be gone.

Apple Support tells me to check the Mail servers, but they are NOT IMAP. Apple Support tells me to restore from iCloud Backup, but it appears that the iPhone POP3 Mailboxes are NOT BACKED UP by the Apple Mail program. Apple has lost my data.

I'm about to convert to Microsoft Outlook which I hope will be more reliable, as opposed to the Apple Mail program which does not store mail data safely.