Number of unread messages in app Mail

Hello

I have 3 email accounts within the app Mail.

The icon says 37 unread emails.

Going to global inbox - filter unread - I get empty list.

Going to search bar - selection see unread messages - the 37 appear - they are all within folders - not anymore in inbox - OR they are older than 1 month.

What the number on the icon is supposed to show?

The total number of unread whatever their folders and age?

OR the number of unread within the inbox?