is it possible to let a web server, for example my Raspberry Pi, start a Script when a specific QR-Code gets scanned from my Mobile Device connected to my Home-Network?
e.x.: I want the Pi to delete spezific data from a Database if the QR-Code gets scanned from a Mobile Device inside my Network.
First of all, QR codes aren't magic.  All they contain is a string of text.  That text could say "Hello", or be a phone number, email address, or URL.
It is up to the QR scanner to decide what to do with the text it encounters.
For example, you could build a QR scanner which tells your Pi to delete data when it scans the text "123abc".
Or, you could have a URL like http://192.168.0.34/delete?data=abc123 where the IP address is the internal network address of your Pi.
Starting Script on Server when QR-Code gets scanned