Lost folders after Outlook update

I know a lot of people have had the same problem : after updating to Outlook 16.21, my subfolders are gone. I cannot even click to open one main email account or the other one. Luckily they are still coming in but all being dumped in the same general inbox. And all the messages that were in subfolders are nowhere to be found.

Late last year a fellow user wrote this :" If you have just upgraded Outlook for mac 2016 from version 15.34 or earlier and have "lost" sub-folders, try clicking on the RH arrow to the left of each folder. This should expand and all sub-folders should be revealed. It is easy to miss this. I did. One minor heart attack later and I spotted it. All is now calm and zen-like. Hope that helps, nick "

I have no idea what the RH arrow is. There are no arrows to the left of the folders I am referring to (the ones identifying the two separate email accounts).

Can't believe this can truly be happening.

Any help much appreciated !

Ann