Sync IO is probably fine on Windows with the exception of CloseHandle, in which case Windows Defender or other AV will invoke a file filter in the kernel's file

Sync IO is probably fine on Windows with the exception of CloseHandle, in which case Windows Defender or other AV will invoke a file filter in the kernel's file I/O filter stack to scan changes for data recently written to the file. A common approach used in Rust, version control software, and other runtimes is to defer file closing to a different thread to keep other I/O and user-facing threads responsive. All that said, I think IOCP on Win32 is a far superior asynchronous programming model to the equivalent APIs on Linux which feel far less usable (with more footguns).