As of now (2.6.3) the durability warning comes up when the item is below 8% durability.
This is, imo, too low.
It should be customizable, since some armors have a low durability in the first place.
E.g. for a Leather Helmet, that means the warning comes up when there's only 4 uses left, which is often too late.

For the default settings, I'd orient myself along vanillas durability bar, which displays its last sliver of red when the durability is below roughly 11.5%.
(For reference, a leather helmet would have 6 uses left. Still not a lot, but better.)

Additionally there should be a bottom absolute value, (e.g. a default of 16, ideally also customizable) for exactly those low durability items.

[Maybe one could also add an even stronger warning, when the durability bar turns completely black (which is below roughly 3.85%)
(15 uses for Netherite Helmet; 22 uses for Netherite Chestplate)
But I am not sure about this idea.]

Has this project been abandoned?

It's little complicate to implement and make great UI 🤔 and I don't have much time for make new features and porting it to all versions

it most likely will be.

I mean, it doesn't have to be a great UI. A simple vanilla style slider/textfield to enter a value would suffice.

Or just being able to edit a value in the config would already be enough imo