It is quite annoying for older codebases in C# that have a lot of existing sync code, but for new code it doesn't matter all that much. You use async methods for IO and DB access and in many applications this means that most of the methods will be async.

I only played around with it a bit a long time ago, but I didn't find Go concurrency as simple and easy as it is often sold. It felt very low level, which is fine for the design goals of Go, but also meant that I was still left with doing some harder parts myself.

Concurrency in C# with async/await is pretty easy for the straightfoward cases that make up most of a typical application. You do have to keep to a few rules and it certainly has very dangerous footguns, but those are minimized if you use consistently use async methods instead of sync.