A partial solution seems to be to view the "per folder" message totals. To do this you need to turn on something called the "message list header" (which is a silly name, because message headers are a completely different per-message thing). Searchi...
That's just a series of animated gifs; it's impossible to see what is happening. As I have already said, on Windows there is no "New Message" button.Nothing in the two screenshots you have posted here shows the total number of messages per account.
Re "In 115, there is a menu next to the New Message button in the Folder Pane in Mail.", for me there is no "New Message" button. This is 115.3.2 on Windows 10. There is a "Write" button in the header of the main Window (the same line as the minimis...
