Unity is easily your best option if you've got any sensitivity to platform targeting issues. They are working on a CoreCLR conversion but no telling if it will actually see the light of day.

The lack of modern c# features and hijacking of things like null coalescing operators are annoying but it's not something that ruins the overall experience for me. The code is like 20% of the puzzle. How it all comes together in the scene is way more important.