was passiert beim formatieren eines usbsticks?

There are 2 types of formatting:

Quick formatting creates a new empty file system catalog. This is virtually a database in which stands as files where they are located in the folder structure, to whom you belong, on which physical memory addresses the file is to be found, etc. Since the occupied and free memory is also managed by the file system, the entire memory is released for use again…

The new catalog overwrites a small part of the old catalog but the majority of the old entries and files are still present and can be restored as long as they have not been overwritten.

The complete formatting creates a new empty file system catalog and then overwrites all free storage areas with NUL-Bytes. So all data on hard drives are safely deleted.

On USB sticks and SSDs there is more memory than the user can use. However, wearleveling generally uses all memory cells and the firmware of the data carrier manages which memory cells were currently provided to the user. The overwriting of such data carriers would not delete all data and very many fragments of data would remain behind!

HDDs also have reserve memory but to a much lesser extent and the reserve memory a HDD is used only when sectors fail during use. More on: https://hackenlernen.com/blog.php?t=hdd_safe_loeschen