duplicate mailboxes in mail

Since updating to Big Sur, I have had a problem with the Apple Mail client. Multiple/duplicate mailboxes are listed.

Have several IMAP mail accounts. All show up in an "All Inboxes" folder under "Favorites" in the sidebar. All accounts are configured the same - Drafts/Sent/Junk/Trash all go to "All [Drafts/Sent/Junk/Trash" On My Mac.

Under "Favorites" there is a folder named "All Sent." Click the disclosure triangle and each of my accounts are listed there. So far, so good.

The problem is that in the "On My Mac" section, there is a separate folder named "Sent" for each account. The contents of these folders is the same as the ones listed in the "Favorites" section.

In addition, there is also a folder "Trash" for each account in the One My Mac section. There is no corresponding "All Trash" collection in favorites or anywhere else.

If I create a draft email, a "Drafts" mailbox will appear under favorites as well as the On My Mac section. If I create a draft in more than one account, a mailbox collection will appear in favorites and separate mailboxes, both named "Drafts," will appear in the On My Mac section.

Drafts and sent both have end up with duplicate folders in Favorites and On My Mac.

Trash just ends up with folders in "On My Mac" all with the same name

Spam/Junk all ends up in account folders on the server, despite the "On My Mac" setting.

This is not how it has worked in any previous version of Mail. Is there a way to correct this?