Hello,
Some months ago, I tried to figure out how to use this I/O port to power a fan and a led strip in my laser enclosure. But I finally drop the idea because I did not find a compatible connector that I could plug on.
But here below is what I discovered about this topic if it can help someone. Of course, double check what is written below, I am not responsible if you fry your Ortur Laser Master 3 
When you look at the I/O port with the reset button on the left, you should have this pinout:
Then you can send M12, M13, M14 and M15 command to change the state of the pins 1 and 6.
Ortur doc says that:
But on my notes I wrote that behavior of these commands is reversed for my OLM3 compared to how Ortur described them, so to be checked on your side.
I also wrote that:
M12, M14 commands make the corresponding pin (1 or 6) voltage switch from 14V to 0V
M13, M15 commands make the corresponding pin (1 or 6) voltage switch from 0V to 14V
And as you said already , I also think you cannot draw too many power from this I/O port.