How do I connect this PWM-controlled supply board properly?

[Demon]

I do not quite follow what you are after. But anyway, the purpose of the optoisolation is to isolate circuits that are in different voltage levels for either safety of the users or the safety and protection of the circuits.

If none of these are of concern at your application, then I see no point in using that module. Connect directly the PWM signal to the MosFet and control whatever load you have.

Ioannis

This circuit was only to provide a fast and easy source of current without worrying about transistor/MOSFET/whatever selection.

If it became my final solution, great, But it was just a way to test PWM LED strips and 7-segment displays without worrying about over-loading a switching device.

I'm doing that now (looking for a suitable L-V MOSFET).