IOS Mail: Unread filter malfunctions in the view "All Inboxes"

The "unread" filter in the iOS Mail app is malfunctioning. This was a problem for me until I found a workaround. Still it ought to get fixed.

I'm running iOS 16.2 (20C65) on an iPhone 14 Pro Max, model no MQ8N3LL/A.

I have four email accounts: iCloud.com, Outlook.com, Yahoo (IMAP), and Gmail (IMAP). I sent one test message to each account and left all four unread. Then I tested three Mail app views without and with the unread filter button at the bottom left corner activated:

• The "To or Cc" view it works properly, and when I add the filter, it hides all the read messages and shows all four unread messages.
• The "All Inboxes" works correctly until I activate the unread filter - then it hides not only the read messages but also the unread messages from the two IMAP accounts.
• The "Unread" view works properly without the filter - it shows all four unread messages. There's no reason for tapping the unread filter button in the "Unread" view, but I did it just for completeness: I expected it to do nothing, but surprisingly it hid Al l messages, leaving an empty view with the inaccurate caption "No Unread Mail"

My workaround until this bug is fixed is to use the Unread view instead of the unread filter.