I'm using opentrack version 2023.1.0 on Windows 11, trying to set it up with neuralnet camera tracking as input and joystick emulation output.

When I tried to configure the output (Joystick emulation -- vjoystick), I get the following popup:

I didn't know I had to install additional software, so I clicked the link for vjoystick.
Then in my browser, I received a 404 error from this page: https://vjoystick.sourceforge.net/site/
I didn't try the direct download link.

By vjoystick does it mean vJoy?
Then perhaps the Sourceforge link should point to: https://sourceforge.net/projects/vjoystick/
Or perhaps a link to the GitHub repository (for Windows 7 upto Windows 10): https://github.com/shauleiz/vJoy
Or perhaps a link to a fork on GitHub (for Windows 11, mentioned on the GitHub page for shauleiz/vJoy): https://github.com/jshafer817/vJoy
Or perhaps a link to a newer fork on GitHub (mentioned on the GitHub page for jshafer817/vJoy): https://github.com/njz3/vJoy/

All in all a bit of a rabbit hole to fall into, perhaps it is better to point the vjoystick link in the opentrack popup to a webpage explaining the different names (vjoystick / vJoy), the various versions, which versions are compatible with opentrack, and when and how to use them.