I code in C# and use a ton of LINQ when writing business logic. It's FP-ish enough to avoid logic mistakes. The mediator design pattern, which is kind of bringing another FP paradigm to the OO world, also features heavily.
I think this is the point really, not that mainstream, "general purpose" languages support FP well, but that FP ideas and aspects have been adapted into many of them.
C# LINQ, being a round-about implementation of do-notation, is a pretty advanced FP feature, and beyond most mainstream languages. C# is certainly a step up over Java etc.
However, most developers wouldn’t understand, say, a result monad implemented via LINQ, so you’re still fighting the ecosystem somewhat.