Outlook Sub Folders not showing

So on a desktop PC Outlook 2016 is installed and there is one pst file being used with one email address. There is a 2018 dated pst file that is open for looking at old emails. Both have many sub folders below inbox.

Uninstalled the 2016 and used the office.com site to reinstall office. After setting up the email account, I tried opening the previously used pst and it no longer shows all the folders under inbox. The mail is still there in inbox but no folders.

I opened the 2018 pst file and it is fine all the folders show. I have a pristine copy of the original pst. I have tried import but got no folders , also tried scanpst and no folders.

I tried the view settings but had no change.

Any ideas on how to recover those folders if it can be done.

I also opened the file on two other PCs with outlook and nothing.

Win 10

Thanks for any help.

pop

I wrote several replies to this yesterday, but abandoned them all after re-reading your post more carefully. When you write "The mail is still there in inbox but no folders", do you mean that old emails that should be there in the inbox are there, but ones that should be in sub-folders (along with the folders) are not present? This may seem a silly thing to ask, as that may be exactly what you mean, but it sounds so unusual I wonder if I have misunderstood.

If the anser is 'yes' then I have no idea - if, on the other hand, there are no old emails at all in the opened file, then there may be possibilities to explore.