How "decompilable" a GMS2 game is depends entirely on how the developer built it:
💡 While powerful for learning and recovery, decompilers should be used with respect for the original creator’s hard work and legal rights. To help you dive deeper into this topic: Do you need a tutorial on how to protect your own GML code? gamemaker studio 2 decompiler
Before attempting to decompile, you must identify how the game was built, as this determines the difficulty of retrieval: Virtual Machine (VM) How "decompilable" a GMS2 game is depends entirely