Why my app use so much GB
Your spotlight database (or worse - filesystem) is corrupted.

I'll link to some other situations that cover this.


About This Mac -&gt; Storage is wrong?
How can I figure out what&#39;s slowly eating my HD space?
Mac OS is reporting bad free space
Noticebly larger amount of free space reported compared to the graph in Storage view


The simplest way to resolve this would be to make a backup (if you don't have one), boot to Recovery HD and use Disk Utility to check / repair your disk. Then you can restart the Mac and let it rebuild the spotlight database overnight. Worst case, you can purge the spotlight database if the situation isn't a transient problem with the calculations.