This made me really curious because I'd not heard of banana bark fiber before. I did some exploring on youtube and found some interesting videos of the process.
The first one features is large scale and uses machinery to help with the process.
This one is how to hand process on a small scale.
Here's one on making paper from banana fibers
And this one is done by someone who started a business in Belize selling crafts made from banana fibers.
Quite interesting, although not yarn I'd use for garments!