Hi Just
I am Dave, I will help you with this.
Did you backup an iPhone or iPad to your drive using iTunes?
Click the link below to download a small free utility called Treesize.
https://www.microsoft.com/en-us/p/treesize-free...
To run TreeSize, right click its icon and choose Run as Administrator.
Navigate to find that 43GB of files and please provide a screenshot of what you find.
If you have any difficulty locating that used space, please provide a screenshot of your C drive in that TreeSize utility, so I can see your hard drive and work out where that space is being used and if there is an underlying problem.