Missing Mail Folders

Suggest reading this Support Document from Apple on Using Favourites in the Mail Application

Te folders might actually be there but need to added to Favourites

refer below

Use favorite mailboxes in Mail on Mac - Apple Support (CA)

As we're not clairvoyant nor can see you Mac P\please read the following user tip and restate your question/problem in detail: 

     Writing an Effective Apple Support Communities Question - Apple Community

What mailboxes are missing. If the missing mailboxes are all from one category in Mail's sidebar look for the arrow to the right of the category and click on it:

Ok then Exactly what has the User Done to try and Find / Locate the Missing Folders

We do not what to offer solutions you has already attempted.