In the official ionCube ecosystem, the "decoder" is actually the ionCube Loader. It is a free PHP extension that decodes and executes encrypted files at runtime.
IONCube Decoder for PHP 7.4: A Comprehensive Guide ioncube decoder php 74 new
When a “decoder” is mentioned
Recommendations
; php.ini
zend_extension=ioncube_loader_lin_7.4.so
opcache.enable=1
opcache.enable_cli=0
opcache.optimization_level=0x7FFFBFFF ; avoid aggressive inlining
opcache.preload="" ; don't preload encoded files
ioncube.encoder.obfuscate_opcache=1 ; if performance not critical