When I make the inbox of an email account a favorite in emClient, the possibility if expanding/collapsing disappears. It’s subfolders aren’t shown.
As far as I am aware “Favorites” are only for a single folder. If you do have that folder under the “More” drop-down listing, what you could do is right-click the folder and select “Show” (instead of Hide) which will move it closer to the top if most of your folders are in the “More” drop-down area (basically hidden). So basically you can hide all the folders to put them under the “More” drop-down, and then SHOW only the folders you want at the top.
Maybe other people here in the forum have other options on this.
That’s correct as @lancealot advised.
Adding an account folder with sub folders underneath “does not show the sub folders as well” if linked to the Favorites. You will only see what’s in the parent / root folder.
Note:- Favorites were never designed to show all your sub folders as well under each parent folder.