> I understand Wine avoiding the flag solution

I don’t - Windows keeps a compatibility database for a reason. It seems inevitable that you’d need to maintain that too to keep apps working or drop support. The performance is a non-sequiter for a few reasons. Even in the hot path the conditional is going to get speculated away since the wine subsystem is uniquely instantiated per application. If you were really paranoid you could ship multiple binaries and select which ones to use dynamically at runtime. I suspect the bigger problem is one of maintenance - Microsoft does this with a huge budget and a huge team whose sole responsibility is maintaining that comparability. A community project is going to have to make more pragmatic choices.