MacOS Big Sur 11 . How do I see the 'Download' folder in 'Finder'

This isn't an issue specifically for Mac OS Big Sur but something I end up searching for every now and again.  I think it probably affects those of us who use Windows and Macs , as searching in Finder in default can be pretty frustrating some times.

Anyway the 'Downloads' folder was happily in the left menu of Finder and then it suddenly disappeared. 
Equally this issue and fix could apply to any of the following Folders. 

1. Recents
2. Airdrop
3. Applications
4. Desktop
5. Documents
6. Downloads
7. Movies
8. Music
9. Pictures
10. Home

To fix this in 'Finder' - click on 'Finder' on the top menu > And select 'Preferences' 

From here you can select to re-add the Downloads folder.