Gmail makes it simple to search for messages that are unread in any folder. This is helpful if you have multiple unread emails across different folders/labels and are unable to find them.
Step 1
In the Gmail search bar, type is:unread and press the Enter key
Step 2
Your unread emails throughout all folders/labels will appear below the search results. Once you have read a message, that message will disappear from the unread email list.