iPhone Back Up Storage I am aware of the two conventional methods of removing an iPhone back up from the computer storage - 1) Through iTunes 2) by directly locating and deleting it using file explorer (on Windows)

Here's the problem:

Last night, I had at least 70GB of free space on my PC's storage. Then I backed up my iPhone, leaving my storage @ 10~GB free space after the back up. After backing up, I decided to remove the back up from the computer since it takes too much space, so I opted for option 1 - which is to remove the back up file through iTunes. However, this did not restore my 70GB disk space, it only left my computer with 18GB of free disk space. I've checked the back up file through file explorer but apparently it's gone already (probably deleted by iTunes). So now I am stuck with an unlocated back up file and 18 GB of free disk space. Hope someone could help me restore my 70GB. Thanks.
Did you recently uninstall and reinstall iTunes from the Microsoft Windows 10 store? If so, the location of the backups may have changed, causing the backup to not be where you expect it to be.

Here's a blog post I wrote with instructions to get to both locations where the different versions of iTunes store the backups on Windows 10. (The different versions being direct download from Apple and download from the Microsoft store.) Hopefully checking the "other" spot will help you find the backup that is hiding from you :)

https://deciphertools.com/blog/where-are-iphone-backups/

If you don't see anything, you may need to allow showing hidden files. https://support.microsoft.com/en-us/help/4028316/windows-view-hidden-files-and-folders-in-windows-10