Only main app I've installed is Fortnite and got an error that I've used 400GB of storage space on my Dell XPS 15 laptop with 0 bytes remaining. The file size of Fortnite was about Link RemovedTemp Mail10 Minute Mail 30GB but even after uninstalling the amount of storage space went down to only 3GB left. When I open up Programs and Features and sort by size, the programs don't add up to 400GB at all (maybe 10GB all up).
Try 'All settinge' from the bottom right corner of your screen, than 'System' followed by 'Storage' there you will find an option to free storage.
Does if free more?
Using 400 GB is not that excessieve, I think, we will see