Haha, my solution was bicycle spokes. Exactly. Cut them to the right length and put a spoke through each of the two holes instead of the nylon. In the end it worked quite well, it lasted a lot longer than the nylon stuff, but at some point they did blow up in your face (material fatigue, it's not really meant for that).
Important: You are the only one within a radius of 30 m and you wear some protective equipment yourself (which is generally recommended).
Also important: You didn't get this idea from me! 🤣🤟🏻 Happy trying

I now use this biodegradable string with a few restrictions (see my review in the product):
Husqvarna Bio X (replacement string, lawn trimmer)

Not so far. Good point about microplastic formation.