iPhone Mail icon - no indication of unread messages

The Mail icon on my iPhone XS Max has suddenly stopped displaying the red "bubble" that indicates how many unread messages are in the inbox. I did nothing intentional to make this feature disappear. I've tried all manner of changes to my notifications in an effort to restore this, but nothing works.

I've tried searching the forum for an answer to this question; I find it hard to believe that it hasn't been asked before. Nonetheless, my search yielded nothing, hence the new post.