By the same token as "Looking at the number of popular games developed with Godot, that would put the attack surface at approximately 1.2 million people", you could say the fact some malware is written in C++ makes anyone who has ever used software written in C++ (~8 billion people) part of the attack surface.
The researchers talk about the possibility that data packs for real games could be infected in the future, but this malware just includes its own copy of the game engine.
Post by the researchers: https://research.checkpoint.com/2024/gaming-engines-an-undet...
Statement by Godot: https://godotengine.org/article/statement-on-godloader-malwa...