Hello, and welcome! We just use the latest version of the game available to us on Steam.

The reason you're not likely able to do the jump is because your FPS is too low. Unfortunately, many speedrunning mechanics depend on either how high or low your fps is. There are some workarounds, however. Many speedrunners use the lowest possible graphical settings so that FPS is maximized. Also, there is an FPS limiter in the menu if that is needed.

Hope that answers your question!

Well, I'm sitting at 80-90 fps atm, while trying to do the trick. I've managed to get it a few times by now, so might just be my timing is off

Yes, like I said, the higher the FPS, the better. I tried it at 80 fps, and while it is definitely possible, it's much harder. Make sure you use the ground that is the highest up.