The previous versions in this stream (.NET Core 2.1, .NET Core 3.0 and 3.1) also run fine on Linux. For web server / API server workloads, it's been stable for a lot longer than 11 months, and people do indeed "bet the farm" or "run the business" on it, quite happily.
Technically, this starts with .NET core 2.1 on 2018-05-30. The prior version, 2.0, released on 2017-08-14, wasn't _quite_ there yet although some people were happy with it for production use.
.NET Core 2.0 (August 2017) we assume.
Have you even seen the benchmarks compared to Java and other languages?
https://www.techempower.com/benchmarks/#section=data-r20&hw=...
If you're not paying attention to .NET its time to get your head out of the sand, seriously.