How hard it is to develop an operating system

Hello everyone, Ebyte here.
How hard it is to develop an operating system ? China still has no domestic operating system comparable to Windows. At present, the desktop operating systems Windows and MacOS are absolutely dominant. It is said to be very difficult to develop? How is it difficult? Ebyte will reveal this for you today. click here :https://www.cdebyte.com/Modem-Serialserver-Singleserialserver