Have a look inside your Documents folder and see if Unreal Projects looks different than regular folders. After a proper link, yours should have a grey link on lower left corner. If it does, it’s linked to a destination folder. Note that even in Windows Explorer title bar it will still say C:\Users\Elyptic\Documents\Unreal Projects even though it’s actually a link.
You can right click and check its properties; there should be a Link Properties tab with “Type of Link: Junction” and “Target: M:\Unreal Projects” shown.
Just watch free space on C:, it’s only way I found out it was working properly first time 