Even sophisticated commercial reverse engineering tools struggle with IC11 unless they operate via a method (which is slow and incomplete).
Before dissecting the decoder aspect, it is essential to understand the encoder. IonCube is a suite of tools used by software developers to protect their PHP scripts from being viewed, changed, or run on unlicensed servers. Ioncube Decoder Ic11.x Php 7.2
The script was encoded for PHP 5.x and is trying to use deprecated functions. You genuinely need an updated version of the script , not a decoder. not a decoder.