Cant see my Documents folder on local hard disk

That is because you have elected (apparently unwittingly) to use "Documents and Desktop in iCloud".

If you click on iCloud Drive in a Finder window Sidebar, there is your Documents folder (and Desktop, too).

If you want to undo this: go to System Preferences->Internet Accounts, click on iCloud. Click the Options button next to iCloud Drive:

Then UNcheck the box below, but be CAREFUL... you will be asked if you want to keep local copies. OF COURSE you DO, otherwise you will lose your documents. I recommend that before you uncheck it, you make a copy of the contents of Documents and Desktop to separate folders in your drive.