Hi and thanks for replying.
I can move mail items to a folder by dragging and dropping. It's dragging to a folder hierarchy I'm asking about. Let's suppose I have folder 'A' on my Mac, containing sub-folders A1, A2 and A3 (in Apple Mail, the folders are called mailboxes, but let's use the term folder for clarity). In its unexpanded state, I see only folder A in the mailbox list. It has a greater-than character to the left ( > ) indicating there are sub-folders. Prior to Big Sur, I could grab an email from the displayed list and drag it over folder A which, after a few seconds, would auto-expand to show subfolders A1, A2 and A3. I could then position it over folder A3 and drop it there. Then folder A would revert to its original, unexpanded, view in the mail list. With Big Sur, I need to firstly expand mailbox A manually, so the mail list shows the sub-mailboxes, then I drag the email and drop it in A3. This Big Sur method is less efficient.
Is there a way to get back the auto-expand feature described above?