OneDrive is not including sub-folders

Hello

I am working from home and have been using OneDrive to store a copy of the work data created on my home PC. I have all work data stored under one folder. I set up OneDrive to synchronise that folder so that the data would always be available online from any computer.

Yesterday, I noted that various subfolders were not even present within OneDrive.

On my PC the folders are set up as:

D:\Work

D:\Work\OneDrive-Company Name

The latter is where OneDrive stores a complete copy of D:\Work

However, I have the following:

D:\Work\IT\Costings\2021\January Purchase

..\January Purchase is missing from D:\D:\Work\OneDrive-Company Name\Work\IT\Costings\2021\  and from OneDrive online.

I decided to unsynch the entire folder by deselecting D:\Work\OneDrive-Company Name in the Choose Folders option under Settings which does not appear to have done anything - it is still present online.

But, when I Choose Folders to set it up again I realise OneDrive is showing random folders to choose from. There is no Folder hierarchy. I cannot see D:\ etc so am unable to choose D:\Work. D:\Work\OneDrive-Company Name is available, but I clearly do not want to synchronise that.

The help links I have seen so far are not applicable to this situation. Can anyone tell me how I can set up OneDrive on my home computer to synchronise D:\Work, please? 

Thank you.