Ghidra (open source from the NSA) with custom MQL4 scripts can analyze EX4 files. However, no fully automated "one-click" solution exists here. This is for forensic engineers, not casual traders.
Finding a legitimate free EX4 to MQ4 decompiler is nearly impossible today because modern MetaTrader 4 builds (Build 600+) are compiled into machine instructions rather than bytecode, making them extremely difficult to reverse engineer. Most "free" applications found online are either Current State of EX4 to MQ4 Decompilation (2026) While historical tools like EX4 to MQ4 Decompiler 4.0.392.1 Free Ex4 To Mq4 Decompiler Software Applications