Both languages/runtimes are decent, stable and good choices for running production systems.
They have different philosophies though, C# is mostly "give the developer a complex toolkit so they can do whatever they want, but keep the runtime simple", while Java is more like "keep the language as simple as possible, and put new features mostly into the runtime making it more complex, but benefiting even old code".
Async vs virtual threads is a clear example of that. The former makes the language much more complex, and has a huge surface area where it may clash with other features, so a developer has to remember all of these. But it's a simple machinery under the hood.
Meanwhile virtual threads don't change the language at all, it's the same as it was with Threads, but under the hood it is a very complex feature.
And in this particular instance I think it is quite clear cut that Java made the correct decision, for the most common use case of these languages having non-blocking IO "automatically" makes for significantly better user experience.