That has been the case since version 3... do you have an add-on providing that functionality perhaps?

tomraymondtom said

Folder list is showing number of unread messages only.

No, I do not have an addon

You can use add-on "EXTRA FOLDER COLUMNS"

 to  display unread messages and total messages in folders.

tomraymondtom said

You can use add-on "EXTRA FOLDER COLUMNS" to display unread messages and total messages in folders.

That was the add-on I was referring to.