Open finder. Up top click go and use the option to type where you want to go. Go to library.

Once there click command + shift + . To show hidden files

Sort by size and then you can start hunting amongst your files and deleting large unnecessary ones!

Last time I did this for someone Fortnite was taking up 95GB despite being “deleted”

What version of macOS are you running ?.. there was a glitch in that sub-system a while back and it was fixed in a particular macOS update.