Generally, API support is not that bad, afaik Unity supports .NET standard 2.0, which is a bit old but not ancient - the chief problem is there's stuff like asy

Generally, API support is not that bad, afaik Unity supports .NET standard 2.0, which is a bit old but not ancient - the chief problem is there's stuff like async/await in .NET which is their standard way of asynchrony, but not really supported in Unity without workarounds. Also the serialization system in Unity tends to interact weirdly with more complex .NET object hierarchies, so expect strange things to happen.