The thing is, you don't really WANT Explorer to do that, because that means it's calculating the size of folders (and all subfolders!) all the time. It will slow to a crawl. That said, I'm pretty sure ...
Windhawk lets you add features, tweak UI behavior, and restore classic elements in Windows, and these nine mods make it shine, from per-monitor Alt+Tab and better File Explorer sizes to taskbar ...