But that's the thing, we're comparing with Go, where all functions behave that way, and no async/await ceremony is required. Go has many weaknesses, but I don't think a language that treats async as unusual/special beats Go in that respect.
I’m am not well educated on the subject though so take that with a grain of salt.
For those curious I looked at Windows and Linux, but not much else.
Linux: no io_uring support. There's debate on even whether to use it as people are discussing security implications[2]. It looks like (from perusing this issue, but could be wrong) AIO wasn't used.
Windows: it looks like they're using IOCP everywhere. Seems sensible enough.
General case: there seems to be an open issue regarding this[3].
[1]: For example, Windows has IOCPs, Linux has io_uring, FreeBSD has kqueue, POSIX has... POSIX AIO, etc.
I was not aware that file I/O isn't async on Linux. Even so, I'm pretty sure network I/O and channel operations (send/receive/select) are async via epoll. I'm not as sure about these, but I think time.Sleep and sync.Mutex.Lock suspend the goroutine as well.