This discussion prompted me to revisit this.
I have revised the SDL version to use SDL v3, which has better Wayland support.
SDL3_net turns out to be a total re-write compared with SDL2_net. Unfortunately the new version is not suitable for Wiznet emulation. In particular the new library has no way of using a known (numeric) IP address without doing a DNS lookup.
Fortunately, reading some of the documentation around the re-write lead me to a site which gave hints on how to write network code which works on both Linux and Windows. So I used this information to revise the coding of the NFX emulation. This now works on both Linux or Windows, using either the native or SDL builds.
The emulation of the WizNet chip is very incomplete. It only supports TCP connections, not UDP or other protocols. But it should be sufficient to support the existing network programs for the MTX.
Note that unless the program is run as Administrator or Root, it will not be possible to open low-numbered ports (less than 1024). The work around for this is to use the switch
-nfx-port-offset <offset>. This adds the specified offset to any requested port number less than 1024.
On Windows, the FTP command line client is not able to connect to non-standard port numbers (the Linux command line client can), but FileZilla can.
By specifying an offset of 10000, and using FileZila to connect to port 10021, it is possible to talk to ftpd on MEMU running on Windows.

- MEMU_ftpd_on_Windows.png (91.72 KiB) Viewed 46934 times
I have
published a release on GitHub including compiled versions of MEMU for both Windows and Linux. Note that this release defaults to MFX emulation, and includes the switch
-nfx-port-offset 10000 in
memu0.cfg, where it will not get overwritten by the configuration menu.