A3.2 and B2.1 in the manual show you the pinouts of that jack and the expected signal, unfortunately section 6.1 schematics and sec D timing diagrams seem to be missing. You’re going to need to find a suitable driver circuit. Without looking at the timing it might accept input from an old MDA adaptor or similar.

https://en.wikipedia.org/wiki/IBM_Monochrome_Display_Adapter

Edit: While this in behind a paywall it looks like this old article has a circuit for composite to TTL monochrome that would be what is needed.

https://www.elektormagazine.com/magazine/elektor-198812/47485

This one is from the 1980s itself and there also seem to be a lot of TTL to composite circuits out there that use fairly modern (and a lot fewer) components so with a bit of looking you might find a modern composite to TTL driver circuit. Look at the retro computer and retro arcade game forums, etc.