partitioning – The system reports 200Gb is used while there is only 40Gb

The df returns 216G out of 512 is used:

 df -t ext4 -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2       468G  216G  229G  49% /

The same data returns Discs app:

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I have checked the files in many way and I can’t find where those 216G are coming from. Example:

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How to diagnose what takes up the space?