The ionCube loader is an obfuscated binary. To decode a PHP 7.4 script, one essentially needs to reverse engineer the ioncube_loader binary compiled for PHP 7.4 to understand how it manages keys in memory. ionCube aggressively updates its loaders to patch memory dumping vulnerabilities. Consequently, a decoder that works for PHP 5.6 will almost certainly fail on PHP 7.4 encoded files, especially those using newer encoding versions (v12+).
Conclusion: If you find a website offering a free "IonCube Decoder 7.4 download," you are about to infect your computer or server. Ioncube Decoder 7.4
You do not need to decode. Install the official loader: The ionCube loader is an obfuscated binary
# For PHP 7.4 (example download for Linux)
wget https://downloads.ioncube.com/loader_downloads/ioncube_loaders_lin_x86-64.tar.gz
tar xvfz ioncube_loaders_lin_x86-64.tar.gz
cp ioncube/ioncube_loader_lin_7.4.so /usr/lib/php/20190902/
echo "zend_extension=/usr/lib/php/20190902/ioncube_loader_lin_7.4.so" >> /etc/php/7.4/cli/conf.d/00-ioncube.ini
service php7.4-fpm restart
The encrypted files will run normally without decoding. You do not need to decode