It would be FANTASTIC if users had the ability to highlight the 1st folder, hold down CTRL- and keep selecting folders. Then, do something like right-click and “Show if Unread” on all 32 folders.
Currently, only way I can see to toggle that option is selecting each folder, individually, and repeat the same function as the last folder.
You cannot do this for the whole folder list, but you can use the “Show/hide folders” window via right-click on a specific account at least, to change the setting for numerous folders at once.