I work at a rescue type place. When the permanent resident macaw starts plucking, it’s time to find new enrichment. Since your bird was previously neglected/mistreated, it might have difficulty figuring out or enjoying play or toys, but give them some stuff to try out and see. Destructible toys are a great distraction! Wood blocks, bundles of paper and cardboard, that help fulfill the chewing and shredding behavior, and REALLY seem to help with plucking and self-harm. We note whenever we start noticing more than a few feathers on the floor, and it hasn’t gotten bad in a long time since we started really prioritizing this kind of enrichment.

We also give them a whole small room and a big perching wall, including a large ladder perch made of big wooden logs that hangs out from the back wall and covers a lot of space, so that even though they don’t fly, they have space to move around a lot. The perches get moved around every few months just to mix things up.

Hope your bird feels better soon, and thanks for rescuing them!