Hey Pylo!
I tried reproducing the issue with the steps you've provided, but I wasn't able to take any fall damage with NoFall enabled. It seems to be specific to your realm or the settings within it.
Can you share any other details or configurations that might be affecting this? Please note that as of Wurst 7.44, it's possible to pause NoFall when you are holding a mace. When this feature is active, it says "NoFall (paused)" in the HackList. Could you double-check that it doesn't say that when you are taking fall damage?
Also, do you have any other mods or datapacks installed that could be conflicting? Let me know so we can figure this out!