this monitor is 640x200, takes 75 Ohm terminated RGB, but 5V TTL H and V sync.
it's kind of a specific standard, i have no idea how it would respond to an emotia input. my best guess is garbage, but it would take someone with more experience to give you a definitive answer.
i think you would have to feed it exactly what it's expecting and i don't know how you can get that source with an actual ST,
or probably there are some other PCs from the 80's that share the video output
I remember the monitor from the early 90s and it should be fine with 15khz RGB. Best case scenario is that you just route the c-sync output to the one of the two sync pins. Worst case scenario is that you need to actively convert RGBs to RGBHV.
I noticed in the spec sheet for that guy - it's expecting 1Vpp on RGB which is higher than normal
If you feed it standard 15kHz RGB signals it should work (provided sync is properly handled) but it will be pretty dark unless you boost the levels a bit