Nitrogen narcosis isn't usually a significant factor in breath hold freediving. They do feel it on extremely deep dives but most aren't going past about 100 ft / 30 m where it becomes really noticeable.

https://alchemy.gr/post/429/dealing-with-narcosis-when-freed...

Technically it's not just nitrogen. Most breathable gasses other than helium have some narcotic potential. This includes oxygen, although the magnitude is unclear. Elevated CO2 levels (hypercapnia) can also seriously reduce your cognitive capacity via multiple mechanisms.

At very high pressures, helium is actually the opposite of a narcotic. This is why it is introduced in Trimix for deep dives. It kind of offsets the narcotic effect of the high pressure oxygen. However it can also cause trembling if there is too much of it.

https://pmc.ncbi.nlm.nih.gov/articles/PMC7478267/

To offset this problem, world record divers are introducing Hydrogen to their mixtures at extreme depths.

https://en.wikipedia.org/wiki/Hydrox_(breathing_gas)

It's not so much about nitrogen and narcosis from other gases, it's that underwater is a dangerous environment where you can get in trouble quickly if anything goes wrong.