iOS 17.6.1 Mail app is not displaying mailbox subfolders

I've discovered a 'sort of' temporary solution!

1. Open Mail
2. The app opens with "Mailboxes", then lists your email accounts beneath.
3. Click on "edit" in the top right of the screen.
4. This will display all the folders you can display under "Mailboxes" such as "VIP", "Flagged", "Unread" etc.
5. At the bottom of this long list is "add Mailbox". Clicking on this blue link will list all the mailbox folders and subfolders.
6. I discovered all the non-displaying subfolders are listed here and can be selected.
7. Click on the subfolder you need to access and it will appear in the list under the "Mailboxes" main title heading. You can then open the folder and access the emails it contains.

Obviously this hack is inconvenient. All the subfolders are no longer logically filed within the mailbox you created for them within the specific email account. At least you can get at vital missing emails though!

I gave up on subfolders. Apple Mail simply can't sustain them reliably. So my solution until Apple actually fix this major problem is simply to create yet more mailboxes per account. Then move the emails from the malfunctioning subfolders to the new mailboxes. Far from ideal, so come on Apple fix this because it's been a problem for several years now and this is basic app functionality.