I don't know if you want to fix the rest of the network.c code at the same time?

ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, ...);
if (ret < 0)
    ret = -errno;

On Windows, setsockopt() - if no error occurs, setsockopt returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.

Here, it just reads errno, which is not updated for Winsock calls.
So this path may yield bogus or zero error codes on Windows.

same as in : network_get_description():

ptr2 = inet_ntop(AF_INET6, &in->sin6_addr, description, INET6_ADDRSTRLEN);
if (!ptr2) {
    err = -errno;
    prm_perror(params, err, "Unable to look up IPv6 address");
}

On Windows, inet_ntop() is a Winsock call, so it sets WSAGetLastError() — not errno.
But this code reads errno directly (leaking bogus data)

and in network-windows.c there is alot of missing error checking in these WinSock functions:

• getnameinfo() Any nonzero return value indicates failure and a specific error code can be retrieved by calling WSAGetLastError.
• ioctlsocket() the ioctlsocket returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.
• select() SOCKET_ERROR if an error occurred. If the return value is SOCKET_ERROR, WSAGetLastError can be used to retrieve a specific error code.

And this Win32 function:
GetAdaptersAddresses() If the function fails, the return value is one of the following error codes (which are outside the POSIX range : https://learn.microsoft.com/en-us/windows/win32/debug/system-error-codes--1000-1299-)

I don't know if you want to fix the rest of the network.c code at the same time?

It would make sense to do so.

ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, ...);
ptr2 = inet_ntop(AF_INET6, &in->sin6_addr, description, INET6_ADDRSTRLEN);

I have fixed both of the above.

and in network-windows.c there is alot of missing error checking in these WinSock functions:

• getnameinfo() Any nonzero return value indicates failure and a specific error code can be retrieved by calling [WSAGetLastError]

The errors from getnameinfo() are ignored so no WSA error codes can leak from here.

• ioctlsocket() the ioctlsocket returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling [WSAGetLastError]

In dns_sd_windows the return value is ignored and in network-windows.c the return value is already handled.

• select() SOCKET_ERROR if an error occurred. If the return value is SOCKET_ERROR, [WSAGetLastError]

Fixed.

And this Win32 function: GetAdaptersAddresses() If the function fails, the return value is one of the following error codes (which are outside the POSIX range : https://learn.microsoft.com/en-us/windows/win32/debug/system-error-codes--1000-1299-)

The return values are never returned as the function calling GetAdaptersAdresses() is only interested in returning the number of sockets.

Additionaly, I found that getaddrinfo() returns errors with naming convention EAI_. While these have the same values as WSA errors (they are simply aliases) on Windows, on Linux the EAI_* don't always map to the errno values. So, I had to create another mapping function that converts EAI to errno codes.
While doing so, I also made sure the return values of getaddrinfo are not fed directly into iio_ptr().

With these changes, no errors outside of [-4095, -1] should emerge.